Like Brett I've run a combo 2 ch/HT for a couple of years now. 1st with a T-8 using the Tape Inputs, subsequently with an Ultra EC which has an EPL (external processing loop). Frank can walk you thru the non-EPL setup. I run the front channels from an Outlaw 990 Pre-proc via optical to the Inday, same from my Denon CDP, then select the source that runs to the Insight+ DAC, and on to the Ultra Pre.
As moeaudio notes in the link, the AVR/Pre-Proc handles the surround, & D-A coversion for the center, surrounds, & sub. I use an Omega 240/3 to power the center & surrounds. What you will need to do with the separate pre is select the chosen inputs used for the HT front channels, Tape or whatever, and select the source channel on the Inday (it has 4 inputs, optical or co-ax) . The Inday has a remote so that's easy, you will need to make the Pre selection manually.
Frank has a diagram in one of the old Audio Basics, if I run across it I'll drop a link. It's worth the minimal time investment for the quality in the 2 channel listening. Hope this helps some.