but I am not asking for advise for what type of control is best in my situation.
Perfectly understand, krassyg, the nature of discussion forums is a free exchange, we're sharing real world advice based on years of experience solving problems with Macs in home theater situations. Many other people will happen upon this thread over time, so I'm sharing some thoughts based on my experience which I hope might help others quickly move past what you're hung up on. They might be faced with a similar issue--trying to control a Mac remotely from a different room--and not be so narrowly focused as you.
I already apologized for not knowing the answer to your very specific "can two BT keyboards be paired simultaneously" question. I won't apologize, though, for advising you to go in a different direction right now--not only to drop the bluetooth and USB dongle dance but also to move beyond a physical keyboard and mouse from 60 feet in your living room. I'm just trying to be helpful, and I completely understand if you aren't able to appreciate my advice at the moment.
I know I can go with the Logitech keyboard and mouse since they are not bluetooth, but I would rather stick with the apple combo.
That might work better for you, I've rarely had reliable bluetooth pairing much past 15 feet but I've read of some successfully using a Logitech 2.4 GHz RF Gyration mouse & KB at your 60' distance and beyond. If you do go this route, please come back and post how it worked in your real world environment controlling your iMac.
(My advice remains, though, for those other than krassyg
trying to control a Mac remotely from a different room entirely: you really don't want a keyboard and mouse in your living room home theater, and why willingly limit yourself to physically awkward remote control of your system from only those two fixed locations? What about the kitchen, the bedroom, the bathroom, the front porch?
So take the $69 you'd spend on a second Apple mouse, the $69 you'd spend on a second KB, the $125 or so you'd spend on a Logitech Gyration, and whatever else you'd be tempted to spend on dongles, cables, extenders and adaptors and put it toward your first iPad. You'll quickly realize what an amazing and adaptable device it is for all sorts of audio and video related tasks, from whatever room of the house you happen to be in and wish you had done it sooner. If you don't already have an iPad and budget is a bit of a concern, don't be put off at all from buying that iPad 2 refurb from Apple, at $319 it's a steal, refurbs carry the same warranty as new from Apple, and that 2 will still be actively supported for a very long time. You'll quickly start using it for much more in the home theater than mere remote control KB and mouse gestures.)