If the M3's are anything like the M22's, I found the full bookshelf design to have a fuller sound in the lower frequencies, you could listen to music without a sub. The onwalls don't have the lower end, so you need a sub.

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB FluanceRT85