help with isolating audio paths

[Plutonique9]

Hey people,
just joined the list, though I've been on AH for a couple of months 
now.

I have a question regarding isolating audio signal paths.
I know that a common use of diodes is for a "one-way" voltage flow, 
yet they don't seem to be working for my application.
I have modified my Yamaha CS-01 to have an External audio input to 
process external sounds through the synths VCF and VCA.
Basically I tapped an input where the CS-01's internal Oscillators 
get mixed into the VCF.
However, I've also been keen on adding a direct output for the 
oscillators. The problem is, I don't want the external signals 
getting processed through the synth to come out of the "direct out" 
for the oscillators, yet as they are on the same signal path, this is 
tricky.
I noticed when putting in a diode backwards, that my noise source 
still comes through strongly (yucky sounding though), so it seems to 
me that a diode may not be too useful for isolating audio signals on 
the same audio path, maybe someone could suggest a better method on 
how to approach this.
Thanks

-- Plutonique9, Plutonique9 at symbiocom.com on 12/24/2000