Any help on Threshold s550e amp?

The heat sinks on the S550e, which I am auditioning, run more than slightly warm and much warmer than the S300. The hand can remain on them, but it will be quite warm. The dealer does not carry the amps you mention, but may have a McIntosh 352 that I can compare. After some extended listening, I will also go back to the S300 to see again what differences I can hear. Thanks for the comments.

Those commens are really helpful. The demo of the Mac will probably not happen for a couple of weeks (a dealer in transition, etc). If and when I hear it, will be back in touch. Thanks again.

Finally. I have now had a chance to listen to both the s550e and the Mac 352. To my aging ears, the Threshold had a tighter bass and just a bit less color in the midrange, but these differences were very slight. I have chosen to purchase the Threshold at a price of about $2300 after netting out the value of included premium cables from Esoteric and a five-year warranty from the dealer. The Threshold unit was used as a high end demo while he was carrying that line and is in mint condition. Even with an aggressively priced Mac 352, at about $3300, to have the Threshold plus an extra $1k left over made it an easy choice to me. Please understand, however. The Mac 352 is a very good amp. With thanks to all who commented and I hope this is useful to others.