I just got my portable cmoy - the smaller model than in the OP. Wow, straight out of the box I'm really impressed. It really is a lot better than the quite standard cmoy that it's replacing, and with the same opamp. The old one was nice enough but comparatively veiled, warmer, imparting less information, a little less width and precision of soundstage (not much but noticeable). The new one really suits my DT990 pros much more, and the quality gap between them and my modded portapros is much clearer, compression artifacts are also much clearer though.
I can only compare it to the one it's replacing, so please take my comments in this context.
Thanks for mentioning this one SpudHarris, I'm really happy.