HT Bypass on preamp

The L/R preamp outs from the prepro go to the HT bypass input on the stereo preamp, so only the stereo pre is directly connected to the amp powering the front L/R speakers for both HT or 2-channel audio.  That's basically it. 

BTW, you don't necessarily need to limit yourself to stereo preamps with an HT bypass input.  Any unused line-level input will work, you just need to set a reference volume level on the stereo pre so it matches volume with your other HT channels (usually use 12:00 when setting channel balance to make it easy).  Anyway, hope this helps. 

The 2ch preamp in bypass mode is simply passing the signal from your processor. In this mode, the volume control on the preamp is disabled so that the A/V receiver volume control is used to drive your L/R speakers and amp. 

Some preamps just set the volume level to unity gain and pass the HT signal through the normal signal path. Other preamps direct the HT inputs directly to the outputs, bypassing the preamp circuitry. You need to look at each preamp to learn exactly what it does with the HT bypass input.