synthrik

I doubt you'd find anyone who'd have dared to risk damaging their precious Deluge like that.

Anyway since it's designed for 9 to 12 volts, I wouldn't feed it 15 volts no matter what.

If you don't need LFO2 and ENV2 for anything else, you can set it up like this:
1. Set OSC1 and OSC2 levels to 50.
2. Set ENV2 to modulate OSC1, modulation amount 50.
3. Set ENV2 to modulate OSC2, modulation amount -50.

Now ENV2 will cross-fade between the samples. Next we'll make ENV2 produce an almost constant value:
4. Set ENV2 attack to 0.
5. Set ENV2 decay to 0.
6. Set ENV2 sustain to 50.
7. Set ENV2 release to 50.

ENV2 will now make OSC1 sound while OSC2 is silent. One caveat is if you have long release time on your volume envelope it will slowly cross-fade over to OSC2 after you release a note. Thus I would recommend that volume release time is set to be relatively short. I would also recommend not to use zero attack time on the volume envelope to avoid clicks at the start of a note.

Next we'll prepare LFO2 to produce a constant value:
8. Set LFO2 shape to SINE.
9. Set LFO2 rate to 0.
10. Set LFO2 to modulate its own rate, modulation amount 50.

Those steps will make LFO2 run very very slow and practically produce a constant extreme negative value.

Now we're almost there:
11. Set LFO2 to modulate ENV2 sustain and...
12. ...learn the modulation amount to one of the gold knobs.

That's it. The gold knob cross-fades between OSC1 and OSC2!

Enjoy!

Maybe this is what you're looking for.
https://synthstrom.com/product/deluge-manual/
I just ordered one for myself as I was getting some spare parts for the Deluge anyway.