First things first, get your SB Touch into your main system. They do sound better than the SB3/Duet, even via SPDIF. Most importantly, it'll cost you nothing.

For me, it would then be depedant upon whether I wanted to improve music, or AV. For AV, try to swap your existing 568.2 for a 568.2mm, then save your pennies for a HD621.
For music, get yourself a TeddyPardo PSU for your SB Touch. Everything I've read suggests that they're definitely worth the cost, and it's now top of my list of next bit of hardware to buy.



861v4/ID40/LPS, HD621, Roon, BAT VK-600se, Impulse Ta'us. Director/Heed Canamp with HD600s.