As noted it is indeed frustrating that many movie offerings are only available in 5.1 or greater. This was a big disappointment when I got the anniversary edition of 'Forbidden Planet', only to realize my old Yamaha HT receiver was surround, but not 5.1, and there was no simple stereo/surround option.
As I haven't listened to a lot of different speakers I can't speak comparatively on the Song Towers verses others, but can recommend the avs speaker thread(s) noted by godawgs. Lots of reading, but lots of good info covering several makes/models in blind listening tests including the Song Towers.
I haven't run my STs in 2.1, and as godawgs notes in his audition writeup my 2 channel/HT area is fairly compact. Front half of a 12x25x7.5 room, narrowed down to 10 wide at the speaker/stereo/HT setup due to bumpout. I'm running the STs in a 2 channel, with a secondary amp/HT pre-processor for center/RR/LR/sub, which also picks up the STs for front L/R on movies. From experience with my system, and what I've read, I don't think you would have any imaging problems or disappointment going simply with the STs. And except for the HT aspect I think the sub is optional.
Size may be consideration given your space, but if the M&Ks are on stands as opposed to a bookshelf or such (not familiar with their size), then the STs probably won't take up much more room. They aren't small, but they aren't huge either. I got mine unheard simply based on the writeups here on the circle regarding the quality of the work Jim produces, and have not been disappointed. I believe I read that Mr VanAlstine runs a 2/2.1 system exclusively, and that would speak volumes to the format given his dedication to quality sound. And in agreement with all, 5.1 while nice is a pain in the arse.
To second a prior comment, you may want to start with a better 2/2.1 channel setup with flexibility to expand it to 5.1 when/if desired. And if you feel you have the room you'd be hard pressed to find a better speaker on all levels at anywhere near the price, and they are a nice looking piece of furniture too. IMHO
speakers: L/R 2 channel & HT-Song Towers, Song Center, RR/LR - Outlaw Bookshelfs