Thanks for the suggestion for the UHA4, I'll look into it!
As for the TF10 and distortion, I had no problems using it with an old Sony DAP as well as the Clip Zip, and with a flat User EQ on the T51. I hope the distortion is not inherent to the TF10, I'm really loving the sound coming from these.
After a good 15-20 hours of use on the T51, I'm warming to the sound more and more, although the UI is becoming increasingly frustrating at the same time.
The good news is, some inroads have been made regarding Rockbox for the Rockchip RK27xx, which is supposedly similar to the RK28xx chip in the T51/S:flo2...
http://forums.rockbox.org/index.php/topic,10428.15.html
Here's hoping...