Sound volume too low, how to increase ST-120 input gain

I'm the second owner this VTA ST-120. I believe this was pre-built order in 2022 with the new face plate. I'm feeding signal from Mcintosh C2700 preamp and sounds great! However, I'm finding gain is too low. My normal listening volume is at 17% for my solid state amp. But with the ST-120, I have to crank it up to 34%. I have a relatively easy to drive Tangband full range speaker, 89db sensitivity.

So my question is how to increase the input gain. Currently it has 3 Tungsol 12AU7 in the driver board and 6550s for power tubes. Can I just replace the 12AU7 with 12AT7 to increase the gain? Or do I need to replace or convert the driver board to a 'high gain' version.

Thank you!

Bragging pic

Thanks Bob!
A little tangent to the topic. If I swap KT120, do you think Ithe ST120 can make KEFLS50 metas sing? My listening level is around 72db.

Ahh around 65WPC, I think that's plenty! I hear people driving it with 30W tube amps, 50W class A solid state amps. I'll play with ST120 for a while, but definitely M125 will be my upgrade path in a year or so