That's because those were original beasts back in the day, with Ice class D power and wolfson dacs.
You will have to stick to the class ab receivers now to keep it under $500. The only class D dinosaurs left are really the older Pioneer Elite and Onkyo RZ from AC4L, but they are $800+ https://www.accessories4less.com/make-a-store/category/avreceiver/home-audio/receivers-amps/home-theater-receivers/1.html?home_audio_key=121-Up%20Watts&brand_f=PIONEER
You might be able to find the last class D receiver from Pioneer, the sc-lx502 on ebay? I think its a 2017 model, good power, most of the 4k feature, if you even care.
Check the deals thread for where to buy and prices, but here is quick summary of receivers available in your price range right now. Since most of the 2019 models will be coming out soon, these are all clearance or on sale. Again, these are mostly new receivers with all of the new 4k features, but all of them have at least LR preouts to add external amps.
Denon x3500h - full preouts, dual zones, digital sources to zone 2 and phono input for the vinyl
Yammy tsr-7850 - LR preouts, phono, dual zones
Pioneer vsx-lx503 - 11 channels total (just in case), good phono stage, full preouts, zone 2/3, good power
Onkyo rz830 - sister to the lx503, good power but just doesn't have video upscaling (if you even care) and it uses the slightly more tweakable accueq advanced
Now if you are looking at just 2 channel playback suggestions, then here is the list of refurbs from AC4L to get you started. https://www.accessories4less.com/mak...ceivers/1.html