The PSR6100 was my second arranger. The first was a PSR70 I think. I used a DX7 for lead sounds, and a drum machine midied to the PSR Later added a piano module and a Yamaha effects unit (for vocal harmony). It wasn't an automatic thing like the Digitechs. I used a midi foot control to assign pitch shifts. I made settings that shifted a third, a fourth and a fifth. You had to know what key you were in, what note you were singing, and what interval was appropriate to call up with the foot control.
If you used to high a pitch, it sounded very "duck-like", but with enough effects it was like having a female harmony singer (who occasionally hit bad notes when I hit the wrong midi button(. This rig replaced a 3-manual Yamaha organ, leslie, etc.
The first arranger I had that I felt didn't need external sounds and drums was the Technics KN2000. (I earlier had an 800 and 1000). By this time Digitech had introduced their Vocalist.
The PSR8000 was the first arranger I had that eliminated need for the external harmonizer. I'm playing that again now, after getting an X1, PSR 740, PSR9000, and Korg PA80, and it still is a wonderful keyboard.
I sold the X1 mainly because the fill buttons were on the wrong side. The 740 vocal input and harmonizer were not up the quality of the 8000. I traded the 9000 for the Korg, then didn't like the harmonizer on it. So I sold it while it was still very new in order to get as much value as possible from it.
I'm looking forward to trying the PSR2000 next. I'm intrigued by it because of the light weight, 4 variations, Cool Sounds and improved harmonizer (over the 740). If that doesn't work it's probably a 9000 Pro, or by then maybe GEM will have a new offering to consider.
DonM