I own this combo. Jeff was on tour in Switzerland about 3-4 months ago and I was able to buy one of the units he played on personally from the importer/distributor. (As an aside, we had a 3 hour workshop with Jeff, which only about 10 people attended because they forgot to publish the date! This was fantastic ... but belongs in another thread.)
This is a beautiful amp. The power output ist 300 watts @ 8 ohms or 500 watts @ 4 ohms. This is on 220v/European standard but I guess the US values won't be much different. There is DEFINITELY no tweeter on this amp. Jeff explained that he doesn't like them and doesn't need one.
There is no issue at all about articulation on this amp. Don't forget, Markbass has some very clever engineers on board and the envelope on state of the art is being pushed every day. You will not miss the tweeter.
This amp has a big boomy low end, as you would expect. (I insulated the floor in my study, upstairs, because the whole house was vibrating and it was driving my wife crazy!) Warm mid range, decent highs. I use the VLE (vintage loudspeaker emulator) filter to mute the mids a bit and it gives me the sound I want. Play with the 4 band EQ, you will get it to just where you want it. (In contrast to most manuals, the Markbass booklet accompanying this unit gives a fantastic explanation of all the controls, allowing you really to fine tune it perfectly).
I just love this amp and can only recommend it. I play mostly jazz, blues and some classic rock, it is perfect for me. By the way, the weight is under 20 kg (about 45 pounds), so relative to it's power it is VERY portable. I am so sold on Markbass that I just bought the Micromark, which is only one 6" speaker, but outstanding for travel!
Tim