In reply to:

I can get the lower frequencies to be nearly indistinguishable (sp), but the trebble still sounds different - the empeg isn't as sharp, even at the highest bit rates.

I have two observations to share.

First, many MP3 encoders will summarily throw out all frequency information above some threshold (typically 16kHz) regardless of bitrate. You might want to experiment with encoder settings (like LAME's -k) that avoid this cutoff.

Second, and let me preface this by saying I don't know how significant it might be in terms of what people are perceiving wrt sound stage and so forth, but I have evidence to suggest that the Xaudio MP3 decoder used in the empeg is only a limited accuracy ISO/IEC 11172-3 audio decoder. This means the reconstructed audio signal differs from a reference signal more greatly than a "full accuracy" decoder is allowed, but the difference is still within an acceptable limit (as defined in the ISO/IEC 11172-4 compliance standard.) The audibility of this difference is undoubtedly a subjective matter, but to the ears of an audiophile, the accuracy of the decoder may certainly have some influence.

-v