Yamaha X4500 (or PSR4500 or PSR4600) questions

[SciNote]

I may or may not be thinking of a change to my keyboard set-up, as I seem to still be getting reverb-related distortion on my current keyboard, a PSR-E433.  It seems someone here recently mentioned the PSR X4500 (or one of its very similar siblings that I listed), and though I should probably have my head examined for even considering a 30 year old keyboard, there is one for sale on EBay that is only about 10 miles from me, and I am a bit curious about it.

I read in the manual that it has a synthesizer mode that allows you to take any of the 100 orchestra voices and modify them.  The manual says that these settings are then saved, so that all you have to do to recall them is to select that orchestra voice, then hit the EDIT button to call up your synth settings.  This sounds like, to me, that each orchestra voice can have its owns unique saved synth settings, for a total of 100 different custom patches (one for each of the 100 orchestra voices).  Is that true?  In other words, let's say you set up a synth patch for sound 01.  Now, you go to sound 02 and hit EDIT.  Can each of these two sounds (01 and 02) have their own unique synth patch, or would hitting EDIT on sound 02 just cause the same synth settings you set in sound 01 to come up?

If this keyboard CAN store a unique synth patch set-up for each of the 100 orchestra voices, that is kind of neat.

Beyond that, how's the keybed?  Some of the older Yamahas were pretty good, as I recall.  And speaking of the synth patches, can they be used in a dual voice?  I know the manual says that, when dual voice is engaged, the two sounds that play are simply the last two orchestra sounds you select on the numeric keypad, but can an edited synth patch be one of the sounds, or can it only be the preset sounds?  And, are the synth patch settings saved to a registration?

I realize this keyboard has major limitations compared to today's instruments.  First and foremost, it only has 8 notes of polyphony, and using dual voice splits that in half.  And as far as I can tell, there is no way to change the octave and volume of each of the dual voice sounds, as can be done on my E433 (as well as just about every other higher-end portable keyboard from Yamaha since about 1991).  And it has a whopping total of 4 registrations available.  Not 4 banks -- just 4 registrations!  Data could be saved on "RAM cartridges", but this was well before the days of flash drives, so these cartridges only kept their memory going by way of an internal battery that, according to the manual, lasts about 5 years and then has to be serviced by Yamaha after that.  Good luck finding a working one of those today!  But some of the features seem kind of unique, compared to some of today's keyboards.

I will admit to a kind of nostalgia/romanticism concerning some of these classic Yamahas.  These came out just around the time that I started working for a major electronics store chain (which went out of business nearly 11 years ago).  These keyboards remind me of the variety that was available in such a store at the time, both in selection of keyboards, as well as selection of products, in general.  Today, I go into an electronics store, and there are no musical keyboards at all.  It seems that all they pretty much sell anymore is just slabs of plastic in different sizes (smart watch, smart phone, tablet, TV).  Maybe I'll someday get one as an auxiliary keyboard.