I feel that I'm probably the person most guilty of promoting the Max and RKV as having the best bass of all the amplifiers I've heard. However, I'd never go as far as to say something like "all DIY amplifiers..." anything. Even within a certain design, part quality and PSU can change dramatically.
What I can say, with authority, is with the META42 in the configuration Tangent built, the bass is very good compared to most amplifiers--but not as good as the Max or RKV.
The RKV is a tube amp so talking about that won't help us much.
Looking inside the Max (there's a pic of the guts on Headroom's site), you can see that most of the power related circuitry is doubled or "split." In other words, the entire power section of the amplifier is dual mono. It's also worth noting that they're using the OPA627, an already somewhat bass-heavy opamp and then running it in AB mode (which I suspect supresses hf details). This combination seems to yield an extremely clean amp with excellent bass response but unfortunately sacrifices a lot in the way of texture and ambient detail to achieve it.
Another commercial amplifier that has relatively good bass response is the Sugden Headmaster. It doesn't quite catch up to the Max, but it's worth talking about. The Headmaster has a completely discrete design but none of if is "split" or doubled. It's also worth noting that in my comparisons, this is the second fastest amp I have heard--second only to the Max.
So... then we have Gilmore's design. Discrete components and able to be run in dual mono. With high grade parts? That could really be something. I wish I could hear one.
I for one am also hopeful about the META42. How much better does the bass get if you stack 3x3 buffers? How much better can it get with the right combination of big and small caps? What about running it dual mono? What about using a Jung super regulated PSU? We don't know these answers yet because the META42 is a new design and hasn't had time to mature with different implementations.
For those of you who expect to be able to best the Max in every way for only $80 in parts, I'm sorry but that's not really grounded in reality. While we could argue about whether the Max at $1800 might be overpriced, if you look inside, you'll know that the parts they chose weren't particularly cheap. This doesn't mean a DIY amp can't catch it in bass response, it just means it may take a little more time, effort and cash.