XLR or RCA cables

How can an adapter double the voltage unless it has a transformer or a powered amp? Either way, it will introduce more complexity and the possibility of imposing something other than voltage on what should be a transparent link.

Since most "volume knobs" are really just attenuators, there is no real advantage in higher output voltage unless the preamp outpput was inadequate.

That is why I started with "I don't know".

A Great Northern Sound PASI unit by Steve Huntley would be ideal if you can find one. Takes RCA or XLR in and RCA or XLR out. I sold one on the Gon and have seen several others for sale over the years.
You could also run a want ad.

This is what you need

Jensen PI2rx Iso Max input transformer. They cost $200 from Jensen. Your RCA cable from the pre goes into the box and an xlr cable out from the box into your amp. The xlr should be short for best fidelity. Short being under 32 inches. The unit is passive so It does not plug in. It is exactly what you need and works like a charm.

I found no loss of fidelity at all. In fact my system sounded better with it as my amp is fully balanced and sounded better using the xlr input and true balanced signal from the Jensen. Amazing little input transformer.

Jensen makes great stuff.