I am having excellent results driving a pair of Nola Viper 1A's with an MC275 IV. However, it took replacing all the stock 275 tubes with Genalex/Mullard and upgrading to the optional AlNiCo magnet midrange drivers on the Vipers to really lock in a musical powerhouse presentation this combo provides. May I suggest that if you are using the SE inputs on the 275, to use Cardas XLR caps on the unused XLR inputs. The increase in resolution is NOT subtle! I'm using MIT2 Bi-wire speaker cables and AQ Cheetah's from preamp to amp with excellent results. Was using AQ Volcano's before the MIT's and while the Volcano's are VERY good, the MIT's nail the spatial coherence, firm up the bass and expand the soundstage in all directions.
It also pays to experiment with powercords as well.
It also pays to experiment with powercords as well.