For amusement only (both of these came from real posts) :

1. Are you sure you took the M60s out of the box ? They do sound muffled in the box.

2. Is there any chance you have a sofa in front of the M60s ?

Seriously, I have both M40s and M60s -- if you like the 40s and you find the 60s muffled, something is *definitely* wrong, either with the 60s themselves or the way they are hooked up.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8