Not gonna get much out of that DP 21" (it's a beast!) with any of the above mentioned amps except the Opti 2000 (decent power, crappy design, may not work long) or the SAZ-3000D. How can you spend so much on a sub like that and then expect it to do good with a cheap $350 amp? I just don't get it.... If that's all you can spend, save another $50, buy a refurb SAZ-1500D from me, and then when you get another $399 saved up, get another SAZ-1500D and strap them together it will beat that bish good! Or trade it in later on a SAZ-3000D... I don't know of any other good amps that will really get that thing moving good for under $350... maybe if you can find a used Memphis 4K cheap or something, though that may be a little too much power on daily use, so might a SAZ-3000D, but if I had one of those subs that's what I would use and try to use some control so I don't smoke the sub....