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Although, I think 400w is overkill in a basement. That thin stream of blood trickling out of your ears is a bad thing. I can't even turn up my 50w guitar amp all the way. I can't imagine standing next to 400w. ....
There are some fundamental differences between a bass amp, a drum amp and a guitar amp.
It's not hard for an amp to drive a speaker with guitar frequencies, drum or bass frequencies (which are a magnitude lower) require also a magnitude more power. If you want a bass that sounds loud enough to play side by side with your 50W guitar amp, he will need about a 200W system.
Same goes for the drums.
Overall the drums can do fine on any occasion with a 100W system, if it wasn't for the bass kick.
The kick (and at times the toms too) require a much more powerful system.
For a practice amp, I would seriously consider a 100W system min!
I've tried playing back on my 2.1 system (2x40W + 1x20W subwoofer) and found it was greatly underpowered, like mentioned, I could hear the padstrokes at the same volume as the vol out of the speakers.
I connected a 200W stage monitor, and found it was definitely loud enough.
If you want to go portable, onstage, the smallest and cheapest you can go is having 2x Behringer B208D amps (~$360 total, plus cables). They are tiny but loud. They also might not amplify the snare a lot, as they are missing out some mids. A single B208D does not provide enough low end to accurately portray the low end of the bass kick though, but I don't know what 2 would do onstage.
A step up would be a pair of B210D's. They tend to have more mids, and deeper lows.
Next I'd suggest the Samson Auro 412 like mentioned in previous reply.
These ones should suffice on almost any stage, for any volume.