I have construct this kit, and if works o.k.
My problem is to adjust the 2 chanels (L and R) super correctly
I propose to give 1 V AC on the 2 inputs and than regulated with de 2 RV so that de 2 leds lichted are on the same high (position). Is that not a better system, than your system?
By the way the VU is constructed with high input
That will also work.