Is the Pisound designed for electric guitar input? The input impedance seems low at 100kΩ - my understanding is that you want closer to 1MΩ for guitar.
Yeah, that is rather low. Most equipment expecting a guitar input will have an impedance of 400k or more. For most-practical purposes, the pickup impedance forms a voltage divider with the input impedance. So a 10k pickup with 100k input would loose about 10% of voltage. 400k would loose 2.5%, 1M would loose 1%.
As a reference, the “high impedance” input of a Fender Princeton amp is 1M, the “low impedance” input is 136k. Some people like the high roll-off that the low impedance input provides.
If you experience “tone suck” where the highs are rolled off too much by pisound, you can use most any pedal before it and that’ll present a low impedance/high output to the pisound so that it won’t “load down” your guitar pickup. A less ideal solution would be to add an EQ plugin to your Mod chain to regain some of the highs that were rolled off.