OK here is a semi-comprehensive look at my experience with Denon D1001 and the Fiio (which is already a part of this thread if you look closely).
Stock d1001 unamped- decent overall, but bass is a bit bloated, mids are significantly recessed, overall sound is bass veiled.
Stock d1001 + stock fiio - even more bass with a proportional increase in bloatiness, highs a little more rolled off, but more or a less similar in SQ with unamped stock d1001s - just different (more bass).
Recabled d1001 unamped- tighter everything compared to stock, bass better controlled, mids louder/clearer and not as dominated by bass, highs extended a bit
Recabled d1001 + stock fiio - bass/mids/highs all lose control compared to unamped, audible distortion especially in the highs can be heard at times (for example putting an electric guitar distortion effect on the sound of cymbals), separation takes a significant hit/frequencies seem to be melting into each other.
Recabled d1001 + fiio w/ new IC (made of same cable/plugs as d1001's new cable) - the difference the fiio makes here is pretty much the same as what the stock fiio does to the stock d1001. More bass but without degradation in separation and clarity.
This makes sense if you think about it logically (assuming recabling the headphones has an effect), because if recabling the d1001 has a positive effect on the SQ, but then you put a crappy little IC in between the source and the new cable / headphones, the result is a more accurate interpretation of the crappy signal gathered by the Fiio, aka a clearer crappy sound since it is less forgiving.
espire, with all due respect (and at the risk of turning this into a cable debate), have you heard a pair of recabled d1001s? If so, then I respect your opinion and humbly disagree. If not, you're just theorizing (which I respect as well), but you never really know what it sounds like until you try it for yourself. -- hm.. I thought you owned d1001s but I don't see it in your sig. I guess I should ask if you've tried the fiio with a decent IC on a quality pair of headphones.