Thoughts on Marantz AV8802a vs Rotel RSP 1582

"2 channel is REALLY important."

Buy a good 2 channel preamp with a HT bypass feature.

"I think using a typical 2-channel preamp is a mistake, because it does nothing to alleviate room effects. The room has the largest impact on sonics, so why not address that?"

That's not good advice. One thing has nothing to do with the other. A 2 channel analog preamp isn't supposed to have an effect on room acoustics, or do any signal processing. In fact, that's exactly why it was recommended in the first place. Providing the components in a system are matched reasonably well, the preamp usually has the biggest effect on the sound that comes out of the speakers. There's better ways to deal with room acoustics than run a perfectly good audio signal through a bunch of crap. Process HT only. Not only that, we don't know anything about the OP's room. Maybe it doesn't need anything.

"Note, you'll also lose bass management when using a 2-channel preamp and speaker level matching and distance delays"

Good. There's no reason for bass management in a 2 channel preamp. If a sub is added to the system, you use the xover in the sub itself for bass management.

Before this turns into a long, senseless argument, consider this. When you go to shows like CES, NY, Rocky Mountain, etc..., how many high end displays use bass management? With exceptions for odd brands like Tact and Meridian, none of them do. In the last 25 or so years, I have yet to see 1 setup that employed bass management.

"My room is small and probably not ideal for acoustics. "

Few rooms are. We all have rooms that are not perfect. That said, I see nothing about your room that should pose any major issues. If a problem does arise, it can be fixed acoustically without spending a lot of money.

"I hadn't considered a separate 2 channel pre due to cost, but now I am intrigued. "

Here's a good article on the subject that goes into a bit more detail. It starts on page 4.