Do attenuators like the Rothwells impose any sort of penalty related to sonic quality?Absolutely they do!!!!!!! I tried these several years ago and they literally destroyed the 3D performance and less so, the dynamics. Horrible horrible horrible solution to reduce the gain. I have this pair in my house somewhere. If I could find them, I'd give these POS's to you for free.
I suggest you contact the company of your line stage and see if there is a parts kit to reduce the gain by 6 db or so.