Hi people, Iīve made an external serial FX loop for my DIY tube combo

Itīs based on a loop called Kleinulator I found on the web, modded by me. Itīs a JFET buffer to adapt impedances for the send preceded by a level control to get the signal to a level suitable for pedals, and a JFET gain stage for the recovery section to get the signal level back up, followed by a level control. All powered by a voltage multiplier (taken from Geofex)to get 31V from a 9V battery or pedalboard power supply. This is to get as much headroom as possible. This is going to be mounted in a stompbox, connected between the ampīs last preamp gain stage (12AX7) and the phase splitter.
Iīve already made it, it works, but I have some things Iīd like to improve, maybe you can help me...
- When the amp is at full volume, the loop canīt take the preampīs signal without distorting. Right now Iīm using it with the return level at full, to get maximum recovery, and the send level at about 1/4 open, with that settings I lose some final volume when itīs connected. At lower preamp levels it mantains "unity gain" when in use. Any ideas about how to get more headroom before clipping (itīs the buffer that clips, the first FET)?
- The loop thins the bass. I guess thatīs a coupling cap(s) issue, can you help me identify wich could be the ones to change? Or is there something else to consider?
Itīs a neat little circuit, and Iīd like it to work as best as possible.
Any suggestions appreciated. Thanks for reading.
(By the way, if anyone wants to use it, by all means do so!)