The Edirol R-09HR is about as good as it gets for under $500, really. Are you sure you've got it set correctly? It won't get dynamics if the limiter is on and/or the recording level set too high. For recording piano, you want the following settings:
Limiter/AGC - Off
Plug-in power - doesn't matter unless you've got an external microphone
Low cut - Off (it's there to reduce handling noise, wind noise, and breath blast when recording speech at very close range)
Mic gain - H
Record level - about 30
If you're recording very close to a piano or other powerful instrument, you will need Mic gain set to L and recording level set to between 50 and 60. Any recording level setting below 28 with Mic gain H may result in distortion even though the 'Peak' indicator doesn't light.
If the R-09HR doesn't satisfy you, you will need very good quality external microphones - think several hundred $ each, and probably a decent external microphone amplifier too.