I owned both of those bikes. You own the M6, so I'll give you my thoughts on the Trail.
The Trail is good bike, but doesn't really do anything great. That's not a negative, just that it's a good all-arounder. It's a little more nimble than the M6 and has better rollover with the 29 wheels. While it's a good pedaler, I didn't find it any better than the M6 which has a lot more travel. To make it a little more fun to ride, I took the fork to 140mm and liked it much better in that configuration. Over our repeated small bump terrain here, I found the rear harsh until I turned the rebound full fast. That one adjustment changed the whole character of the bike.
The Trail was also the first time I ever understood how people could feel the stiffness in a frame. That bike felt solid and was super fun on runs where you could really pump without a ton of repeated hits. For a 120mm bike it was very forgiving.
I bought the Trail specifically for some of the more XC trails. I wanted a bike that ripped, but could also handle the bonus drops and terrain that they have. The bike handled the features great, but just wasn't as good a pedaler as something like a Yeti 4.5 or Ibis Ripley. When I went back and looked at times on those trails, I was amazed that the Mach6 was actually faster than the Trail. It seems there was just enough chunk on those trails that a little more travel would smooth it out.
At the end of the day, since I have more than one bike I ended up selling the Trail. It always seemed that one of the others was better at the trail I was going to do. If I only had one bike, the Trail would be a great choice. That said, the Mach 6 is better I think. Other than wheel size, I don't really see anywhere that the Mach 6 gives up much to the Trail. And it's nice to have the extra capability when you take a poor line or don't execute a move as well as you thought.