+/- 1 would be too low for a lot of people.
On OS's with a integer-based audio structure that would be the absolute max anyway. I think that on OSX you'd clip the dac when the master volume would be set to unity gain and ChucK would go beyond +/-1 anyway.
Basically you'd just end up with two more multiplications, I think. It doesn't really matter what we call the reference level anyway; it's just a matter of perspective relative to the final soundsystem.
Yours,
Kas.