all HT receivers I'm familiar with have pre-outs and will work the way you are asking. The key is this - you want to feed the main outs from your receiver through your your SP-12 preamp in what is called "bypass" mode, and have your main speakers/D-90 amp connected to your SP12 pre-outs.
This setup allows you to use the same main speakers for 2 channel music, and alternately for HT with a simple change of switches. It's not likely to make your HT Fronts sound a lot better (due to the Receiver preamp limitation), but can't hurt it, and greatly simplifies the speaker setup for you.
I doubt your SP12 has true bypass, and if this is true you set up the receiver to feed main outs into a free input on the SP12 (eg tape in). You then set your SP12 volume at a set point that can easily be remembered (eg 12 o'clock), which is where you set it any time you use your HT. Calibrate your HT speakers with the SP12 at this level. You will need to have your SP-12 powered on whenever watching HT. When you want to listen to 2 channel music, simply leave your HT receiver off and run your source through the SP12 as usual.
You can search the archives on "HT Bypass" and find a lot more discussion on this. This is not biamping - which isn't what you're asking about.
As for HT receivers - you should state your budget range if you want some good recommendations. I have a Sherwood Newcastle which was cheap and is stunningly good given what it cost me (~$150 used/mint), though it has some shortcomings.
