You can actually do this very easily. First, you put together the 2-channel music rig. So, connect the Triangles to the output of the integrated amp. Also, if you have a dedicated music source such as a CD player, connect its analog outputs to the integrated amp, ie CD>Integrated>Speakers. OK, now you have a good 2-channel music rig.
To integrate the HT receiver into this, it is helpful to have an integrated amp with an HT bypass/processor loop, but it is not absolutely necessary.
OK, for HT, connect the pre-amp outputs from the Rotel into the HT bypass inputs (or any unused input if no HT bypass loop) of the Integrated amp. Connect the center speaker, surrounds and LFE subwoofer to the corresponding speaker outputs on the Rotel. Connect any HT sources (DVD, VCR, Cable box, sattelite receiver, etc) to the inputs of the HT receiver. That's it.
So, for 2-channel listening, you just turn on the integrated amp and source component and enjoy! For HT, also turn on the Rotel and push the HT bypass button (or just select the corresponding HT input source if the Int. Amp doesn't have HT bypass loop). In this setup, the volume control of the Rotel will control the volume of all channels.
The HT bypass loop basically turns the integrated amp into a power amp, thus bypassing the pre-amp control functions of the the integrated. If the integrated amp you buy does not have an HT bypass, you would simply need to set the integrated amps volume to a pre-determined position (maybe top-dead-center) each time you use HT.
I have had several setups exactly like this over the last few years. Some integrated amps that I owned were Arcam Alpha 10, Anthem Integrated 2, Plinius 8200. Each had an HT bypass/processor loop and they all worked well.
Although this may not be EXACTLY what you asked for, it is truely the best of both worlds as the 2-channel rig is totally unaffected by the HT systems potential sonic shortcomings. But in this setup, the integrated is powering the front L&R speakers regardless of wether you are listening to 2-channel music or 5.1-7.1 channel HT.
I hope this helps. Feel free to e-mail me if you don't understand the information in this post.