[Richard L]

I see, the HFS6 does have an IDC trimmer but not the HFS-4. It uses pre-amplification instead.

We feel having the fixed PA gain is easier to set up. We have found user end up wearing out the IDC trimmer before an ideal PA gain is determined.

On the HFS4, you can use the PI-R as the H6's IDC trimmer, provided you do not use the MPS input. If you want to reduce flow, just turn the PI-R trimmer CCW.

You seemed to know the aquamist system very well.