Saluki is correct, and really, if the selling price diff is around $250 (which is what I've seen), I think it might be worth it.
That said, if I already had an M6, I don't think it'd be a big enough deal to take a flip hit to purchase one. I was able to craft a lot of different tones with the M6 EQ. It's deceptively simple interface control a surprisingly flexible tone stack. You just have to not be afraid to really use it all. But on a new purchase, I think the M9 is the sweet spot.
Big plus 1... I rock the M6 and find the voice control and tone stack to be very useful in achieving different tones as I play in very different bands- roots rock and dub/electronica.
I love the M6 and it's plug'n play capabilities, and have zero gas for something different.
