Help with upgrade from Marantz 6011

If your the kind of person who likes to continue to upgrade then separates is the way to go. If you just need a little more power and then your done...then just get a receiver 

Do you listen to multichannel music or is critical listening more 2-channel?

Never listen to multichannel music.  That's all 2 channel.

I’d keep the Marantz (it’s probably fine for HT duties) and buy a good stereo integrated amp and incorporate that into the system.  By hooking the 6011’s front L/R preamp outs to an unused input on the integrated (or HT bypass if it has it) and then connecting your 705s to it you’ll have a pure 2-channel rig within a HT system.  When you’re listening to stereo the Marantz is completely out of the signal path, and you can switch between stereo and HT simply by changing the integrated’s input.  If you’re looking to up your 2-channel performance, this is the best and most cost effective way to do it IME.  Hope this helps, and best of luck.

Thanks for the advice I really appreciate it.

What do you think of adding two 5 channel amps?  I found on CL near me someone selling 2 Rotel RMB-1085s for $900 for the pair.  I can use the Marantz as a processor and then the Rotels to power my setup.

Will this work?  I'm ok to buy used just trying to sort through the large number of options.

Thanks again