As stated just recently, the Hartke 7000 actually has two independent 340W at 4Ohm amps which can either be two full range amps (same signal and freq range going to both amps) or biamp with crossover points between 80Hz and 2.5KHz. Here, I googled it for you
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That is a great amp. I had a 3500 which is basically one side of it. They are heavy, but have a reputation for being reliable. You can upgrade the 12AX7 tube on the preamp side as well (I did on mine) and might have to as that is pretty much the weak link as they do wear out.
For the cabs, you will get advice on TalkBass until you are too old to play on what cab to get. However, there are some fundamental truths that will always be a good guide. Every speaker (not the box, the raw driver) is designed to operate in a particular frequency range and will perform differently in different boxes (cabs) that range from optimal to dismal but usually somewhere in the middle. These days there are 8" drivers that are designed to go deeper than some 15" drivers so as stated earlier size and freq range is not really a consideration. Also, speakers are designed to respond to the amount of power you send them differently which is measured in dB and called sensitivity. What that means is that two speakers given the same signal from the same amp will provide different amounts of volume if they have different sensitivities. As a general rule of thumb, the cheaper the speaker the less sensitive it is and therefore does not make the most of the power you send it - ironic since players on a budget need to make the most of what they have. Finally, there is no free lunch and especially in bassland: cheap and low and loud and light and small does not exist - you can have a couple of those features simultaneously but then the others are out of whack (ex. cheap and low, but not loud or light or small. ex. low, loud and light but you will have to pay $$$$$).
Now, on the mixing cabs/speakers etc. - it's a box of chocolates. You get players telling you that all kinds of combinations sound good but in my opinion everything I've had sounded good until I played through something that sounded better. Also, just because some manufacturer produced it doesn't mean it was any good - if that were true everything that ended up on a music store shelf must have been awesome. What will happen for sure is that if you have combined two speakers that have different capabilities and behaviors, as you work to dial in your sound or push the volume to keep up with a drummer etc. one of the speakers will likely be coasting and one will be running on the ragged edge (but that may produce a certain tone that somebody likes...). Regarding my statements above, combining two 210's could be as unpredictable as combining a 2x8 and a 115 if the cabs aren't the same - not the same brand but are tuned the same, respond to frequencies the same, etc. For example, the Hartke 210 Transporter, VX210 and 210XL are quite different cabs but they are all Hartke 210s. I personally wouldn't mix those cabs any more than I would a Hartke 210 XL and a Hartke 115 XL (and I did for a while and thought was awesome at the time... mostly because it sounded better than what I had before).
Try to go with what you have for now, if you are new to figuring out connections and the resulting resistance (8Ohms, 4Ohms, etc.) be sure to ask advice so you don't let the smoke out of your rig. After that, save up and read a bunch of these threads and get around and play through and listen to as many rigs as you can. The most expensive cab isn't the one with the highest price tag but rather the one you didn't need to buy or don't like. The best values are on used gear but you have to learn what to look out for. There are gems and dogs out there from every Brand so read up a bit before taking the plunge on something.
In general you get the most mileage out of multiple cabs with the same drivers (exact same, not just same size) whether it be 10's, 12's or 15's. There are exceptions but they are just that, and not the rule. On the real cheap there are some standard cab designs that are out there and you can buy raw high quality drivers (Eminence, Faital, Dayton, etc. but you need the full TS parameter specs on whatever you buy to properly design the cab for the driver) that can get you great performance but you need wood working skills or know someone who does (and can follow specs and not get creative). If you don't want to build something, then you need to hear the cab(s) you intend to buy. Don't go on advice - everyone loves what they love and often conflicting advice can be confusing. If someone loves a particular rig the only thing you can know for sure is that it works great for them - but different players have different tastes, needs, budgets, gigs, etc. etc. etc. Also, don't bother listening to people's recordings of their cabs on 'da tube etc. because how the cab sounds on there is more a function of the capabilities of the recording equipment. Also, there is a wide range of players on TB - from guys who couldn't imagine playing through a rig that didn't cost at least $2,000 to those who could never justify spending $2,000 on a bass rig to their wife.
On bi-amping... it isn't really out of date but for some reason players think it is harder to have more knobs and cables on top of your cab than on your pedalboard. The thing that really changed is the notion that you should just put a 15 on the bottom and a pair 10's or 8's on the top and call that effective biamping. Again, referring to my statements above speakers are designed to work within a range. A given speaker can do an incredible job over a narrow freq range or a less incredible job over a wide freq range, but there is no magic driver that will do both. So, effective biamping is when you pick speakers that compliment the freq range of each other (say a 15" that runs out of steam around 1000Hz and a 5", 6", or 8" driver that will run happily down below 1000Hz and then crossover around that freq so that one picks up where the other leaves off). If you match two cabs that have hugely overlapping frequency ranges and then biamp them you will not be utilizing large portions of the frequencies that either cab could be producing which is inefficient. Many expensive cabs have different sized drivers in the cab and use a passive crossover inside the cab to accomplish this, which is basically accomplishing the same thing only after the amp instead of before it.
Then again, this is just another one of the endless TB Amps section recommendations. Good luck with journey to cab nirvana
