Is it worth upgrading from Denon X8500HA to JBL Synthesis SDP 58?

I would suggest the Anthem AVM90 over both of them. The ARC is pretty intuitive and not difficult to run. There are a few people out there that will take you ARC file and tweak it further if you don't want to.   

I  have an Anthem MRX 540, which shares the room correction with the AVM90.  I’m disappointed by the results, the noise and the poor Dolby Surround controls, and lack of USB digital or Roon, and lack of direct analog. 

The noise to be fair is barely audible but shows up on my measurements, it’s enough to keep my amps on when they should go to sleep. Dolby Surround doesn’t work even when it says it is (2 channel Netflix), and quite frankly the room correction didn’t do much, but at the same time didn’t give me the controls I needed to fix things. 

If I was choosing today I’d pick the Marantz AV10 over the Anthem.  Built in Audyssey, Dirac available, built in Roon.  I used to be a huge Anthem fan.  I may actually switch back a generation, I think the old Anthem processor sounded better. 

I have not herard the OP’s other choices. 

As long as you are comfortable with having professional calibration, and the JBL gets good reviews and exceeds your needs (room for growth, both your system and you), it makes sense.  I'm all about easy, and would be leery of investing in a processor that benefits most from professional intervention.  I didn't think I would make any changes to my HT, then I did, and having to call a pro back to tweak the system would cause me grief.  I had a Marantz AV8805A and then developed an urge to upgrade.  Looked at higher end processors (upwards of $10K) and given various factors (i.e., the good but not great audio quality of streaming, whether the greater investment in "better" equipment would be evident in my system, the depreciation of equipment due to technology improvements) decided to go with the Marantz AV10.  There is much to like about it, not least of which the on-screen menus are a blessing, their documentation and support is very good, it is rock steady, and setup using Audyssey easily and readily provides better than out-of-the-box sound.  It also offers a Dirac Live option, albeit at additional cost (included in the JBL).

Good luck.