You might not EVER need to "upgrade" your mains from the M22's to M80's if you have a decent sub. They are wonderful speakers.
Are you located in US or Canada? It seems to matter quite a lot relative to cost and availability of both receivers and subwoofers.
The EP125 is an entry-level sub, and you might be able to get a big more performance for the same money depending upon your location and how heavily you weight appearance. Outlaw is selling what looks like a
solid little 8" sub for $159. If it had a built-in crossover, I'd buy one for my office. Since you'll be using a HT receiver, you won't care about a crossover in the sub. Other budget sub options include the
Sealed 10" A3S-250 from Elemental Designs for $350 shipped and the
sealed Ultra sub 10 from Emotiva for $289 shipped.
I've been recommending the refurb Onkyo receivers all week - you can get the
TX-SR508 for $179 plus shipping.
It's a good plan to spend money to get quality main speakers like the M22's. That will make more of a difference than anything else.
Have fun!
