Very curious indeed...Over the weekend I got the Signature version (from a fellow Audiogoner-so burn in should not be in play)of my current M III amp which per several reviews was said to be a significant improvement. When I replaced the M III with the M III "Signature" it was not the major improvement I expected, and the bass was very wooly , boomy. The mids and highs, while very good, were no better than the standard unit. Since I am using anti-cables and of course had to disconnect and reconnect them to switch out the amps, this thread caught my eye. I have been playing for about 24 hours now with no change. I am about to switch back to the former amp and am very curious to see if things return to normal...