Here's the deal on receiver vs speakers for budget.
Receivers/amps have been around a long time. The design of them is based on a very mature technology. While there are minor improvements regarding features, the basic performance of a receiver today is essentially the same as 10, 15, even 20 years ago. Similarly, the differences between Marantz, Denon, Yamaha, Pioneer, etc are slight. All should do a fine job of converting a line level signal to a speaker level signal with minimal (not audible) distortion and without coloring the sound by emphasizing some frequencies over others (in other words the reproduction is neutral).
So choosing a receiver gets down to the power requirements of your speakers and what features you want/need.
Speakers, on the other hand, rarely sound the same! IOW, whether your system sound good or bad is really dependent on what speakers you choose (assuming you did not buy some POS receiver - Pyle comes to mind, but they might not be too bad for all I know).
If you were setting up a $2000 (or more) stereo system, I would say 80% $ for speakers and 20% for receiver.
Unfortunately, in your price range, you bump up against the minimum cost of a legitimate receiver. The link below is my favorite place to buy AVR's on a budget. Most of their equipment is refurbished, but the important thing to understand is that they are refurbished by the manufacturer (Marantz, Yamaha, etc), and sold by Accessories4Less who has been approved by said company to sell their refurbs. Also note that all refurb units have a warranty from the original manufacturer.
http://www.accessories4less.com/make-a-store/category/avreceiver/home-audio/receivers-amps/home-theater-receivers/1.html?
The key thing to understand is that the manufacturer has kept his involvement in these refurb units.
You did do well with your Marantz purchase. This Denon might save you about $50 and offers a little more power, but not worth losing any sleep over (and I think the Marantz looks nicer,
)!
http://www.accessories4less.com/make-a-store/item/denavrs700w/denon-avr-s700w-7.2-ch-x-75-watts-networking-a/v-receiver/1.html
For speakers, if all you had to spend is $100, you bought what I would have recommended! However, I would encourage you to spend more to get the AA's, because they will give better sound plus much more bass (without being exaggerated). The designer of these speakers is Dennis Murphy who is retired and follows his passion for music and sound by playing in an orchestra and building high value speakers for people like you. He has his pension and is neither trying to build a business or even earn a comfortable living from his speaker sales...oh, and he just happens to have a gift for designing crossovers to bring out the best in the drivers he uses!
Here is where I reviewed his AA's:
https://forums.audioholics.com/forums/threads/new-2015-affordable-accuracy-speakers-by-dennis-murphy.95661/#post-1092558
https://forums.audioholics.com/forums/threads/elac-b5-vs-philharmonic-affordable-accuracy-new-monitor.97171/
To answer your question, you can indeed use your BS-22's as mains for now then make them surrounds later. I don't know how long it will take you to be ready to upgrade, but I can say that spending the extra $125 for the AA's will give you good quality sound. The BS22 is lacking in bass (as would any speaker with a 4" woofer) and has some coloration of the higher frequencies. The AA also has more bass than the FS-52 (Pioneer tower) and has a cleaner, more transparent sound. The AA's are fine speakers to listen closely to. I cannot say that about my BS-22's (which I gave away).
Here is a thread from a guy who was looking in a similar price range as yours:
https://forums.audioholics.com/forums/threads/need-a-little-help-upgrading-sound.97381/
Yes, I'm giving you a hard sell on the AA's, but they are that good!!!
