I own a pair of M60s, so take what you read next with a grain of salt.
I don't find them bass heavy, at any volume. Even if I did, I could always trim the bass response using the EQ on my receiver.
That said, if the goal is to put together a top notch home theater over time, then the M60s are a really great place to start. Here's why: You can buy them now without the need to pick up a sub. The M60s bass extension is quite good. In fact, I often listen to my M60s on "pure direct" (no digital effects or in receiver cross-over muddling) and find the bass punchy and direct - no muddines - and the treble to sparkle quite nicely.
Then, later, you can pick up your sub, your center and your surrounds as funds become available.
If, on the other hand, you think you'll be content with the M22s (and perhaps want to save a little money in the long run on the whole HT), then pick up a set of M22s. Augment them with a sub (or not) as your budget dictates. Many on the boards have found (and this sentiment is echoed above) that the M22 + subwoofer is a pair that is hard to beat.
Remember, there's the risk free in home trial to fall back on. I have complete confidence that you'll be satisfied any route you choose.
