If it sounds okay to you on the built-in speakers and headphones but not in an amp, then the problem is the amp. An amp should sound at least as good as the on-board speakers. Piano is the hardest thing for an amp to do well. I don't know about all the Bose L1 models, but the L1 Compact is not a good choice for piano. Roland amps are not great choices for piano... most are terrible, some are okay, none are great. Higher end JBLs can be quite good for piano, low-cost JBLs are not. If you're looking at budget powered speakers (say, under $600), check out any of the models from Electro-Voice (especially the ZXa1), or the Alto TS308 which is surprisingly good for the money. Maybe the QSC CP series, I haven't heard those. I also haven't heard the JBL Eon 600/700 series, they might be okay, but my guess is that those others will sound better, I generally haven't found recent JBLs to be competitive sound-wise until you get to the PRX series. If your budget is higher, QSC K8.2 is another good choice.