The 610 is loud and sounds great but I don't believe in pushing them terribly hard due to the way they are wired (two of the speakers get a lot more wattage, leading to blown speakers if you beat it up). It will not put out the low end of a 410HLF either.
Edit: I am fixing this post. Turns out I am wrong about the wiring of the 6x10 and it uses 6 ohm drivers. I hope that is correct but I do not know for sure that it is -- I know a LOT of people have blown the bottom two drivers in the 6x10HLF and I suspect there is a reason for that - possibly that section of the cabinet is tuned differently, I do not know. Based on the schematic I think this is the case.
8x10's are junk man. They work, and some people like the sound but they're poorly designed and I expect the only reason people like them is because it's what they are accustomed to. They're anemic in the low end, don't disperse well up top, and weigh 3x what you need to have to put out that much sound.
The problem I think you're running into is that the 410HLF has a huge frequency gap between around 600hz and 3500hz leading to getting lost in the mix very easily. Combine that with the Ampeg's mid scooped nature and you have a recipe for MUD if you don't eq to counteract it.
I see that you have two options.
1) The 410HLF with the SVT-4 pro should be enough volume to compete with a loud unamplified drummer or a half stack that is not pushed insanely hard and is willing to eq around you. Sit down with your guitar player and tell him:
We need to EQ out slots for each other so we can be heard in the mix. I want you to stop boosting your lows and your highs and run closer to 'unity' and I will do the same, then we'll eq around each other.
You need to work together to develop a mix sound, not just each try to get your tone separately. Sounds that sound good in the mix very often sound like crap alone, and vice versa.
So, work on mix tone and stop relying on pure chance. I would suggest you start with this as a guideline:
You should be cutting some low lows, boosting your low mids a bunch, cutting your mids a little and boosting your upper mids a little, possibly.
Your guitar player should try cutting some bass, boosting his mids and treble.
That's where I'd go as a starting point and see how it works.
Get your drummer in on the mixing down process and be absolutely sure that:
a) You do not swallow the bass drum
b) The guitarist does not swallow the cymbals and snare
2) Continue competing in the volume wars. You have more than enough amp to win any volume war with a guitar player but you need a much louder set of speakers capable of better top end extension and more sensitivity to do so.
Here are some recommendations:
a) Buy my Dr. Bass 3080 (it's cheap and will be way louder than your current rig and go higher) from the classifieds
b) Order a pair of LDS 115/6's and bridge your amp into them.
Bottom line though,you have plenty of rig for your situation, and you will get far more mileage out of making your idiot band mates listen to you and work together than you will out of buying new gear to fix a nonexistent problem.
