I have toyed with the idea of aftermarket cables for my HD 560, though putting $100-200+ cables on a headphone that I paid a quarter that for on Ebay is a bit questionable. If I did so, it would be for just a shade of warmth without losing resolution (possibly gaining it if the cable were better than my original one). But I see that cables are very controversial on Head-Fi, and since I've never tried, financial caution sends flashing lights.
I believe that is a wise move, particularly given the prudence you have shown in selecting an amp. Its easy for some on Head-Fi to forget that some of us have bills beyond an invoice from HeadRoom :)