I am looking for a 2-channel to power my M22's. Looking to spend around $300 - $400. I am also using a HSU STF-2. Any recommendations would be greatly appreciated.

From the two you listed I like the H/K 3480 as the best for the money. The STF 2 in black is out of stock but they still have the silver in stock. If you would rather have a black sub look at the new VTF 1.

Grass, welcome. Of the two that you mention, the 3480 is a very powerful unit and would be more cost effective(around $270). Since you are already using the STF-2 sub, let me also suggest that you consider a HT receiver rather than two channel. Not only would this allow for flexibility for future use of surround speakers for greater enjoyment of two channel music material(using DPLII etc.), but it would immediately have bass management to properly divide the burden between the M22s and the STF-2, instead of running the M22s full-range. Possible candidates in the $300-$400 range would include the Onkyo 604 and Yamaha 659.