Terry, welcome. The first point that I'll mention is that rather than getting a center speaker immediately, the M2s could serve at least temporarily to form a "phantom" center. Your budget at this point might be better spent on a bargain sub such as the Hsu STF-1(little over $250)or surrounds such as the QS4s.
Your speakers don't have any unusual power requirements and many of the reasonably-priced receivers available would do just fine. The 6040(around $250-$300)should certainly serve you well. However , let me suggest a more full-featured unit for just a little more: the factory refurbished Onkyo 605 is available at
Shop Onkyo for $349 if you register for "Club Onkyo", plus you receive a $10 credit and free shipping, so it's $339 delivered.
