I recently upgraded from the 2006 HeadRoom MicroAmp with Desktop upgrade - to the 2007 Ultra MicroAmp.
One major difference is that the 2007 Ultra is transportable in that it requires a power adapter and has no battery capability.
I talked to the guys at HeadRoom quite a bit before I made the purchase and they said that compared to my current 2006 MicroAmp w/ DT upgrade the following is true:
1. The 2006 MicroAmp with DT upgrade has a little better sound quality and components than the standard 2007 portable MicroAmp.
2. The only battery powered "portable" solution that would provide a significant sound upgrade for me was the 2007 Portable Desktop Amp with the 'deeply' class A home module ($1000)...
3. While keeping the same footprint but foregoing the battery powered portability factor - the 2007 Ultra MicroAmp would provide the "significant" sound upgrade that I was looking for.
With all of this in mind I went with the 2007 Ultra MicroAmp. I listen to my music at home in my easy chair and during work at my desk. In both cases I can use my existing +15V DC power adapters. The battery and portable factors were never a big issue for me. Now they don't even exist!
After listening to the Ultra MicroAmp with my iPod Classic 160 and UE-5c for a couple of weeks I can say without hesitation that I don't mind being tethered to a wall wart...THE SOUND QUALITY IS AMAZING! I thought I had an awesome little setup with the 2006 MicroAmp but the 2007 Ultra MicroAmp raised the bar for me ten-fold!
I'm not very good at writing comprehensive audio reviews but I can say that I am soooo glad that I went for the 2007 Ultra. It's an amazing little piece of electronics. The detail, sound stage, bass, treble, mid - everything is so precise and accurate but still remaining super warm and fun. This amp really does it for me that's for sure!
I think it's worth every penny of the $700 sticker price. I am now considering putting my 2006 MicroAmp w/ DT upgrade along with the PowerEx batteries and charger up on the for/sale forum.
Hope this helps you out.