Aries has a volume control. A software one.
Vega has a volume control. A Hardware one.
They are not related. If you disable the volume control in the Aries, it will not affect the one of the Vega.
The Vega volume control is always enabled because it’s a hardware one. You have to avoid the Aries Volume control, it’s a software one with some degradation in sound.
Yes the Vega can be used as a preamp. But at 100% the signal is untouched (like the volume control is just a wire). If you plug the Vega to a preamp or an integrated amplifier, you must use it at 100% to have the full scale signal.
If it’s too much for the preamp or integrated, you have to use the Vega volume control to avoid clipping with your preamp/integrated (for eg if 4.8V with XLR is too much for your preamp, because the standard is 4V)