Preamp with two volume controls?

The Audioprism Mantissa had two volume controls, one for each channel. I believe it was a true dual mono design. Mark Levinson bought the rights to the preamp and amp designs and marketed them under his Red Rose brand. I owned and used one for twenty years. With an outboard power supply with a heavy duty umbilical and four tubes it was a very sweet preamp. It lacked a remote and it did not do spatial relationships the way my ARC Ref 6 does but it was still a very good preamp at the price-point. Incredibly quiet and reliable. Tubes lasted at least 2000 hours, even 3000. 

You might think about how this 21 band equalizer, separate L and R could help you.

It is also a line level source selector if that is any benefit, sometimes placement location makes that useful even if it duplicates existing line selector

I believe Pass Labs made a totally dual mono preamp (XP-30) to the point where each channel has its own head unit which shares a common power supply (3 boxes in all).

Could the Hi-Fi maker in FLA be VAC?

I'm confused or you're confused. 2 preamps give you 2 x 2 channels. A preamp with 2 volume controls gives you 1 x 2 channels but with separate left and right control.