I did in-depth listening & comparisons of the JAR 650 vs a stock HD650 last year & realized 2 things: I'd never heard an HD650 before--but when I did, became a fanboy. Other headphones are better in this or that sonic attribute, but I can't think of another this good overall at this price point I could live with either, but preferred the JAR 650 for its incremental improvements over stock. IMO the JAR 650 mod extends almost everything good in the stock HP, w/no sonic penalty I don't hear the hardness in the bass that you describe; perhaps it's there, but I don't hear it. As for brightness, I hear the mod as more detailed & resolving than stock, but tonally quite similar. Both stock & mod sounded quite good on every SS amp I tried, and predictably scaled up in the usual subtle ways on an OTL, my favorite amp for these headphones.