The PM800x was voiced with a VERY!!! weak lower treble upper mid
I have the PM8005, my speakers are the Monitor Audio Silver RX6. I find the sound very balanced.
Most of the time I have it in "direct" mode, if I do anything with the tone controls, it is to add abit of bass, depending on the recordings and where I am in the room.
So, for me the treble balance is very good, no problems with it lacking or being agressive.
I have a few very nicely restored marantzes (2226B, 2220, 1060) and I don't find their sound that different.
The 8005 sounds very clean, you can just turn it up and up and it stays clean. I'd say a bit too clean maybe, lacking a bit of "rawness" ?
For one year I was using my CD6005 with the PM8005, but when I started using a Rega Apollo CD player, I realised the amp is more capable than I thought.
The 8005 places the instruments quite precisely in the sound field, voices can be really nicely centered, but it sounds less "3D" than my 1060. But the 1060 will not place instruments and voices as precisely.
I like my 2220 because it has that "untreated" raw sound. Maybe I just like some more distortion, who knows...
And yes, any vintage Marantz will not sound its best before a good restoration, IMO and from my personal experience.