The Eroica used to come with the Music Hall 7.1, as I recall, so it's a good match with Project arms. I never heard the M3, so I really can't answer your question. Without an audition, there's no ironclad way to know whether you will prefer the Eroica to what you have, but it is a really nice cartridge. Unless you're working with a good dealer, audio can be a lot of hit and miss. I frankly thought that the Goldring that came with my Music Hall MM5 sounded really good. I think it was a Goldring 1012 or 1022. If your 5.1 isn't pleasing you with the stock cartridge, maybe you have to look elsewhere in your system. I don't know. Maybe you should call Needle Doctor. They sell the Music Hall turntables and they probably know what works and what doesn't. Maybe. One thing I've found in this hobby is that truly knowledgeable analog people are very few and far between. IMO