Do you have a multi-channel HT system currently or is it only 2-channel? If you wish to have a multi-channel system fronted by the Rotel processor and have the desire to "add-on" a better 2-channel rig for music, you are probably going about it backwards.
The way I've always done it (and received lots of confirmation of success on this forum) is to set up the 2 channel rig first, i.e., music source->preamp->amplifier->speakers. Then add on the HT buy running the L&R front pre-outs on the HT processor into an HT/processor bypass input (or any unused analog input, like aux) on the preamp. Then connect HT sources and LFE output (if used) to the HT processor and run interconnects from the HT process to the 5 channel amp to power the center, surrounds, etc.
This setup works great for music as there is no (zero) HT components in the system when you are playing music. The pre-amp will control the volume in this situation.
When you want to play HT, simply turn on the HT processor, select the associated input on the 2-channel pre-amp (the one where the L&R front inputs from the HT processor connect to the pre-amp). If you used an HT/processor bypass loops, you can totally disregard the volume control on the pre-amp as HT bypass is a unity gain (0+/-). If you used and unused analog input, like aux, you will need to always set the volume of the 2-channel pre-amp to a "pre-selected point" like top-dead center or "full power" before calibrating the speaker outputs and again everytime you play HT. In this situation, the HT processor controls the volume for all channels.
It is much simpler that the post may indicate. It is especially easy if your HT processor has an HT/Processor bypass loop. It is designed exactly for this situation.