If you want good Amiga audio, you need an Amiga. Even with a large sound buffer, UAE's sound output is really nasty. It's also really hard to "play along" using the keyboard because the timing's so dodgy.
My A1200 copes great with OctaMED Soundstudio (version 1 of which is now freeware) and it cost me £60 :-D
That way you also get the secret Amiga X-factor.
(I'm just wondering outloud here then when I ask if anyone knows: Will Soundstudio run on A1/OS4?)
:-)