In case you didn't know this, the analog output of the UA5 is after your input passes through the a/d and d/a converters and another gain stage.
While the a/d in the ad500e is good, you're introducing additional noise and coloration from the UA5's d/a and output gain stage. I would think you'd get better results just recording from the UA5.
I realize you plan on using the ad500e from a different preamp and just want to try running it, but I just wanted to point out this isn't an ideal setup and might not be a good "test" to see how it sounds. You're actually comparing the UA5's a/d to the UA5's a/d + d/a + output gain + ad500e's a/d.
I ran an ad500e for over a year (changed to v2>ad1000, v2>mod-sbm1, v3, wmod-UA5). Nice unit, but I have serious doubts its a step up from the wmod-UA5. Definitely depends on the preamp you'll use with the ad500e, but even if close, the UA5 wins for functionality/ease of use.