We run the SP16 w/ Quatros and various amplifiers and source components and the gain is usually fine. Without knowing how much output your source has and the input sensitivity of the Classe's, I can't be certain, but yes, 8 db is a big difference and should help.
The only recent ARC preamps to offer adjustable gain were the LS25's and the LS26.
The only recent ARC preamps to offer adjustable gain were the LS25's and the LS26.