Just upgraded from an X4000 (7.1) to X4500 (9.1) and I've been pleasantly surprised with the sound quality improvement.
The surrounds appear more detailed and louder contributing to an overall fuller sound quality and sound-stage.
Granted this isn't 1:1 as I am now using Dolby upmixing vs. Neo:X, added 2 upfiring fronts and the calibration wizard is more detailed.
I was never sure if the mic positioning sequence mattered with the X4000 and I don't think I measured all positions before.
Overall the upgrade seems worthwhile for audio improvement combined with getting my video spec support up to date.
The only feature complaint would be lack of ALLM (for now) especially since the X3500 already has it.
Onto the issues - Lemon alert! I connected the X4500 on Friday and I now have no sound at all.
Everything worked great after initial speaker setup (9.1), level testing, mic calibration, firmware update, etc.
On Saturday I tested all my HDMI devices, watched a movie, YouTube, Netflix. All good.
First thing Sunday morning I decide to poke around the menus and made some minor tweaks.
I can't recall all the (seemingly innocuous) changes, but I did notably discover a misconfiguration of the upfiring speakers as in-ceiling, and I enabled center spread. No audio was playing at the time.
Upon starting the test I was confused that the receiver wasn't sending audio to the speakers. No physical changes from the previous evening.
Oddly, audio signals are detected correctly for all inputs, all functions are acting normally including video output, however the speaker levels menu is totally unresponsive. Tried a known-working USB stick and Internet radio but still no sound with the track timer proceeding as expected.
Fed up, I saved my config to USB and performed both the menu factory reset and eventually a front panel microprocessor reset.
Same problems in both scenarios starting from scratch or loading the USB config.
Curiously the setup assistant has the same problem with the speaker level menu. The relay clicks when you are ready to test, no sound and nothing responds (cannot select yes/no for sound signal validation), but you can press the back button which clicks the relay again.
I've seen a lot of threads citing the headphone dust issue but this is a brand new device! The H/P input isn't displayed on-screen and since I don't have an adapter I'll try a vacuum or blower later today.
Hopefully this isn't an indication of reliability as I've seen other reviews citing similar lemony issues. I've arranged for an exchange in the meantime but curious how others are doing since release?