I wouldn't get a microtrack. They do record in 24bit, but I really don't see the point of 24bit unless you have a "reference" quality playback system. They also do not record more than 2GB at a time and the cost of CF cards is an issue.
The iRiver will work fantasticly with the UA5 running digi in.
If you want something that will sound substantially better than your stealth rig, you might want to look at Josephson, Beyerdynamic, Peluso or MBHO. Even more impressive are DPA, Schoeps, and AKG480's....