I would still think with M2's you would use direct mode, as it shuts down other un-needed functions on the receiver to make a more pure sound. In Direct mode the sub still works, so I would think it would be the same for smaller speakers. As long as he has speakers set to small, and has his crossover set correctly, he should be good to go. He may have to bump up the crossover to 120hz or so since he is using bookshelfs.