Here's my answer to the same question in another forum:
The other main difference is that the D1 has two DSP processors (double the processing power) and up-sampling of all digital inputs. The big advantage to me of the dual DSP's would be the extra power available for future upgrades. When Dolby intro'd PLIIx, it required either: no chance for firmware upgrade due to lack of DSP power; or change out of DSP to be able to implement (AFAIK). Having this extra DSP would help to alleviate some concern about future upgrade paths.
The upsampling is advertised to improve sound quality on standard (non hi-rez) sources. And to my ears it's really working. Listening to the difference between the analog inputs (with no upsampling) and the digital input with upsampling is like night and day. Imaging is much more precise, soundstage is much wider, better high end clarity with less "edge". AND, the upsampling is also working on regular DD and DTS signals, and the D1 is the first pre/pro on the market doing that. And to me it was a nice surprise, because to my ears, this is also making a nice improvement to something I was taking for granted...
Nick from Anthem told me that the D1 is the "hot-rod" version of the AVM20/AVM30 people where asking for. The digital stage was totally redone and is presently second-to-none on the market. The analog stage is almost the same, with some minor changes. The D1 is to be used with the digital connection to flex all his muscles, and the analog stage was not their priorities. With the upcoming firewire connection (i-link), the awesome digital stage of the D1 will then be used at full capacities. The analog stage of the AVM20/30 was already really good and almost totally transparent, so there was no need to change it. If it ain't broke, don't fix it!
Here's a quote (Gordon McGregor) I did found in another popular forum. I know the implementation is also really important, but for those interested in specs, this sums it all pretty well.
"DACs AK4395, used in D1, are day-and-night in comparison with AK4382, used in AVM20, the first ones are in the top line together with the best multi-bit delta sigma DACs, and used in such stuff as Tag AVR192, for example ... therefore they sound significantly better then just a bit above average AK4382 ... ADC are top-notch AK5394A, those are used in Lynx Two B (one of the best professional sound cards) and also are one of the best if not the best available ADCs ... therefore they will sound better then used in AVM20 AK5383, the last ones are 24/96kHz and a bit worse then the newer AK5394A ... op amps are OPA2132P vs OPA2134 in AVM20, those are a bit worse (IMO) concerning the sound quality, but in D1 they used the special low offset voltage version of OPA2132 by purpose, I don't know exactly what is it, but can assume that they got rid of the coupling electrolytic capacitors in the path, it means in such circuit OPA2132P can sound even better then OPA2134 with average level of electrolytic coupling capacitors. Two DSP56367 vs one only make the DSP process more flexible for D1, it looks like one DSP makes formats decoding, and another one - post processing ... then it is better again in D1. And finally - AD1896 can significantly improve the sounding of D1 in comparison with AVM20, it means that D1 is a REAL upgrade vs AVM20 ..."
And 2 reviews of the D1:
http://www.hometheatersound.com/equi...atement_d1.htm
http://www.hometheaterhifi.com/volum...04-part-1.html
And some details about the upsampling:
http://www.soundstage.com/gettingtec...ical200408.htm
