One Expression pedal to control 2 Eventide pedals

No experience with the Boss, but can’t you hook up the expression pedal to it, instead?  The H9 & TimeFactor can remain set to Thru.  Could be a problem if the TF & H9 have to be on different MIDI Channels, though.

I use the Boss EV-30 expression pedal with two outputs running into two H9’s. A simple $99.00 solution. The midi expresion from my ES-8 is problematic into the H9’s.

Two ways to achieve this:

First way: Plug your expression pedal to your ES5, and map it to a MIDI CC message on your ES5, so it can send this CC to two H9s, and map this CC to control volumes on both H9s.

Second way: Plug your expression pedal to the first H9: 

1. Set first H9's midi output to MERGE (so it can thru and transmit its own MIDI messages).
2. Turn on the first H9's MIDI CC XMT
3. Set the first H9's MIDI XMT CC mapping for the expression pedal in the XMT CC menu (by default it is CC 11)
4. Map this CC message to Expression pedal on the second H9
5. Now you may use your expression pedal on both H9s. If you'd like to use is to control the input or output volume, you may set it on a preset by preset basis. You may do it in H9 Control by clicking "More" and "EXP controls input volume" or "EXP controls output volume"