Steve,
When I purchased my 990 several months ago, it replaced a Parasound AVC-1800 that used Burr-Brown PCM 1716 DAC but unfortunately, Parasound designed them to only to resolve to 24bit 48kHz and not the full 24bit 96kHz range the DAC is capable of. Similar to your AVC-2500, the Motorola 56009 processors used as your DACs resolve to 24bit 48kHz. The 990's DACs can take full advantage of the 24bit 192kHz recordings now available. You will hear a big difference if you have SACD and DVD-A discs like I do. For CDs, the difference is less. Haven't heard the AVC-2500 recently so I can't comment how big a difference you will hear but there will be positive difference I think if you go with the 990. It certainly was with my AVC-1800.
Slbenz