My take on this, having auditioned the M22's (but not the EP175, so take this for what it's worth), is that they are very neutral, musical speakers. I was able to blend them (with some effort) with a much larger sub than the EP175 and get good results. For movies, I think you're far better off with monitors and a sub, than just towers and no sub. Music is a bit trickier, though.
The frequency chart on the M60's is quite flat, as speakers go. You will get neutral (accurate) sound from it's entire rated frequency range. While that range doesn't go down to the nether regions that a good sub will bring to the table, it goes down far enough for most music, and will be a better balanced sound overall, in my experience (with different high quality, full range towers).
I still have the same struggle between towers and sub/sat setup. In the end, I chose towers because I plan to listen to a lot of music in bypass mode on my pre-pro.
Another potential advantage to full range towers is that if you do add a sub for movies, you can still run the front L+R in full range mode which can help smooth out the bass response in your room. One problem with a single sub is that you can't escape the "hot" and "dead" areas.
