A good receiver with pre-outs will be a starting point. In the Marantz series, the SR6xxx and equivalents in Denon / Yamaha could work nicely. I have a Marantz SR 7010 and I use it in pure direct and also with the crown xls 2502 power amp. I further have a separate DAC - Pre - Power setup. The Marantz on it's own does not fall short as far as its ability to drive my Quad S2's go and I am pretty happy with all three setups. The sound signature will be different of all three but all three work just fine and to my satisfaction.
The concept 20's are easy to drive speakers, so a decent AVR should not have problems driving it. You could always add a power amp in future if needed.
Lets assume that you have this integrated amp that you really like and you want to use it in your setup for stereo, if this amp has a HT-bypass, then you could connect all your stereo music sources to the integrated and use it in stereo mode as well as use it's HT-bypass feature to use it as a power amp to drive your Left/Right speakers for Home Theatre use.