What Ant said - I use my receiver for 5.1 and for stereo. It's an old amp now, and has a button on the front to force whatever you're putting through it into stereo. Might be best to download the manual from the manufacturer's site if they do one and check from there...
I have the Onkyo HT-R393, it has a different menu set-up to Ant's, but does exactly the same thing in letting you choose which speakers are attached to it. Until recently I only had front left and right connected, due to moving and being too lazy to run speaker cable where I needed it, and had the amp set to 2.1 without having to change any of the source audio.
Onkyo seem pretty popular and I remember when I was looking fairly priced. No issues with mine. Got a reasonable deal on it a few years ago. Never actually bought a decent speaker setup though.
I joined when I got my amp. Meant I got whatever percent they were offering at the time, plus another £10 and it was on sale. I don't think the guys behind the counter (I actually went into a real shop!!) appreciated all the reductions I got.
I think they make so many things, even they've probably lost track - musical instruments, motorbikes, ATVs, electronics... Mind you at least they're not Samsung, those guys make rather large boats (e.g.: ferries) as well :-&
Anyway in terms of being a fanboi, I tend to prefer Yamaha to Onkyo and DM (Denon-Marantz, same mothership); but if you go quite a bit further up, then Anthem and a few others rear their head as well.
I just want my music to sound good and be able to hear the dialogue in 5.1 sources, where both sky box and raspberry pi fuck up the down mix so much I have to adjust the volume every two minutes.