I have a 2500, but the 2550 and 2500 are essentially the same player from a hardware standpoint.
As for your first question, the fan noise is not excessively loud, however I'm a good 15-16 ft. from it. The only noticable noise it's mechanics when it's attempting to read/load a disc, the transport isn't terribly quiet, but this is typically only noticable when it initially starts up or after a disc is inserted, I've never noticed it while a feature is playing at all.
As for the firmware, it's fairly obvious when you're playing a standard DD/DTS track as opposed to the DTS HD-MA or Dolby TrueHD. Unless the equipment is fairly low-end or budget HTIB, the difference between the lossy and lossless formats are relatively easy to distinguish.
Not to be a d*ck, but just because you didn't get a response in less than a day, might want to be a little more patient. AH obviously doesn't garner the traffic for video source equipment that AVS does, but they also don't have near the trolls. I'm sure others w/the 2550/2500 might chime in here, just might take a little bit...
-TD
