Help! Receiver or preamp? Im overwhelmed...

The OP asked for help on the receiver/preamp side of things, so I don’t think we should be overloading the response ledger with disc player recommendations.  So any, a few observations.

1) Budget is important, as others have noted
2) Latest HDMI?  First of all, that is a moving target, as all of us have to deal with.  It changes frequently.  Otoh, since you are willing to buy used, that can be an advantage.  Many a consumer has moved on from a perfectly good component because the HDMI standard has changed.  If your monitor, disc player, and other sources are happy with an older standard, then you will have quite the market to choose from.
3) Consider Room Correction.  IMO, this is the biggest sonic advance in HT over the past 20 years, particularly if music is the main priority.  For me this narrows the choice down to three companies: Anthem, Yamaha, and NAD.  Anthem and Yamaha use their own proprietary RC, and NAD uses a third party, Dirac.  I haven’t heard a NAD, but I use Dirac from another vendor in my 2 channel system and love it.  I have 2 Anthem 5.1 AVRs (MX 520) both were huge upgrades over the Onkyo and Pioneer ES that preceded them.  I heard the Yamaha demoed at my dealer and it wasn’t as immersive as Anthem but it is very good with dialogue.  Again, your priority is music, so I’d go with Anthem

mahler123:" The OP asked for help on the receiver/preamp side of things, so I don’t think we should be overloading the response ledger with disc player recommendations."

Hello mahler,

     Did you not read my entire post or did you just not understand my proposed solution that goes above and beyond his original question and is likely much easier on his budget, no matter what the OP states it actually is, as well.
     An Oppo, combined with his existing 5 ch amp, would outperform any a/v receiver or preamp/processor that I’m aware of. He also gains an excellent universal audio and video disc player with a built in video processor, if he doesn’t have one already.
     I’ve never had the issue of an outdated HDMI input or output with either the Oppo 105 or 205 and doubt the OP would either.
    The only downsides of using an Oppo 105 or 205 as a preamp/surround sound processor are the following:
1. Atmos is not supported.
2. There is no auto room correction.
3. If vinyl playback is required on the system, a separate 2-ch preamp is needed.
     The OP said he only uses 5.1 surround audio for HT. room correction is seriously overrated and, if proper care is taken in selecting and positioning all speakers and subs in the room, it’s not necessary in my opinion and I’m waiting for the OP to state whether he uses vinyl as a source.

Tim

Get an Anthem AVR.

I say this because it's cheaper than their HT processors with 99% of the same parts.  The big difference is the AVR only has RCA outputs.

So, even if you decide to keep using your Emotiva amp, you save around $1k.

Thank you SO very much gentleman! I should also mention I will be keeping the Rotel (Not that it matters). As for the budget, I'm guessing up to $1000 would snag me an excellent unit in the used market? I do not play vinyl so that will not be a concern.

As far as video I'm guessing I want to be able to upgrade to a minimum of 4k handling ability, correct? And honestly, to play music we use either a Playstation 3 and 4 for discs and use it to access the internet for music sites and use the optic connection to the receiver. We even use an old Toshiba HD-XA2 for upconverting old movie content and some audio through it as well as it has a Burr Brown Dac. Use Playstation 3 and 4 for online music, movies, games etc. 

So yes, this boat has oars and we are probably missing out on a lot! For heaven's sake, I'm still using my speakers with one set of cables instead of Bi-wiring. So I need to learn about that too...Shew, work, and family have made me quite illiterate in the HT game, but I'm keeping faith there is potential!    

Would a Marantz SR5014 or SR7012 be a good choice? Or would the audio not be as satisfying as Rotel? What older Anthem unit would be a good choice? I like music to be very dynamic and hard-hitting...

Marantz NR1510 UHD AV Receiver...What about this? Since I have an XPA 5 Amp?