Yamaha CS80

Speaking about pedals, I like the way I can control vibrato-depth on 
my Oberheims with a footpedal. I know, the CS80 has aftertouch to act 
as a source for vibrato-depth but I find it difficult to use this on 
chords.

I was thinking, there is an external input for the sub oscillator. 
What if I take a sine-wave and use a cv-pedal to control the 
amplitude of that wave (using a modular synth's oscillator and vca) 
and feed it to the sub-osc ? Can I control vibrato-depth ? Does 
anybody know what the maximum voltage is that may be fed into this 
input ?

Why did Yamaha implement this external source ? Did they have a foot-
pedal available that provided a controllable sine-wave ? I never use 
any pedals with the CS80 but if it could control vibrato-depth I 
would use all the time ;-)

And I have another question concerning the portamento: when I set the 
portamento-time to long I notice this has effect the ribbon too. When 
you slide your finger across the ribbon and let go, the pitch goes 
back to it's origin in portamento-style. Is this normal

Concerning the detune slider. My CS80's are tuned extremely tight. 
When I set the slider at zero, there's allmost no beating between the 
channels (I like that). To set a usable detune, I have to adjust the 
slider just a little bit. I can't understand why Yamaha gave this 
slider this wide range.

Well, all those questions. Still, the CS80 is my favorite synth. I 
discover new sounds all the time. I'm now into the 2 channels detuned 
sawwaves, the CS80 can compete with the Oberheims on these sounds.