Connecting the H9000 to a guitar amp using the 4CM is all about matching the proper impedances going in and out of the amp. Remember that the H9000 first and foremost is a high-end studio effects processor, and almost always prefers to run at +4dBu for optimal results. With the 4CM, mitigating noise outside of the H9000 is just as important because unlike a studio environment where we would typlically run balanced signals, with guitar rigs, we're forced to run unbalanced cables in and out of amps and effects loops. Also, you have to study what kind of signals your amp's effects loop prefers and this requires a bit of trial an error. Experiement with running signal out of the H9000 at -10dBv or +4dBu. For my project, short of commissioning a custom interface, which has been the norm for most touring musicians who have used Eventide studio processors in live guitars rigs, I chose Radial J48 direct and Reamp boxes, because of all the ones accessible to me, they offered the best features (pads, phase reversal) and most QUIET signal of all.

To start, I began trying to achieve consistent volume with the H9000 in the loop bypassed or engaged. I also compared my signal without running it into the amp's effects loop; my Mesa/Boogie Rectifier 25's have a switch that allow me to turn the loops on or off. I do this to ensure I'm preserving volume consistency and preventing any tone suck. The next challenge was figuring out a way to combine the H9000s FX Chains. As of this post, we're currently not allowed to do it internally. I chose the rackmountable RJM Effects Gizmo because it allows me to engage FX Chains as if they were loops on a pedalboard, but most importantly, because it allows me to maintain balanced signals in and out of the H9000; moreover, the Effects Gizmo is switchable via MIDI, which I paired with their powerful RJM Mastermind GT16 floorboard for maxlimum control. A side note: there is a version of the Effects Gizmo that runs entirely balanced, which would be optimal to run more than two H9000 FX Chains together. For my rig, I chose the stock Effects Gizmo, which has four balanced loops (9,10,11,12), enough for two effects chains.

My signal flow is as follows:

1. Guitar into the input of the RJM Effects Gizmo. On the back of this unit there is an output "from the front" that I connect to a Radial J48 DI to convert the guitar's high-impedance signal to low-impedance. I connect this to the H9000 XLR input 1.
2. Inside of the H9000, I split the signal from XLR input 1 and feed it to inputs 1&2 of FX Chain 1, which I will feed the inputs of my amps. FX Chain 1, therefore, will be all the effects I want to send to the front of the amp, typically all gain-based effects like EQ, compression, drive, distortion, pitch-shifting, wah, and some modulation.
3. I take the outputs of FX Chain 1 out of the H9000 using hardware outputs 1&2 via DB25 and into the loop Returns, 9 for left,10 for right, of the RJM Effects Gizmo. This requires a DB25-TRS 8Ch snake. I use Mogami. I then take RJM loop outputs 9&10 into the front of the amps using humbuster cables. Because amps do not accept balanced signals, you'll have to run channels 1&2 of the H9000 at -10dBv and use this humbusting cable that allows for noise rejection with devices with regular, non-balanced inputs. You can make your own by taking a regular TRS cable and simply re-soldering the Ring tip to the shield or ground on one side. Connect the re-soldered end to the amp. Best-Tronics also sells them. Note: You can adjust the H9000 analog reference signals (-10dBv or +4dBu) in stereo pairs by pressing the Setup button and adusting "analog refs". The same can be found on Emote.
4. From the amps' effects loop SEND using regular unbalanced cables, I connect to a Radial J48 DI boxes to go from a high-impedance signals to low-impedance signals. I take the XLR out of the J48 boxes and into loop Inputs 11&12 of the RJM Effects Gizmo. I then take loop 11&12 Send of the RJM into H9000's channels 3&4 via another DB25-TRS snake.
5. Inputs 3&4 of the H9000 are routed to FX Chain 2, which will process my amp's effects loop, typically all time-based effects – delays, reverb, modulation, etc. I keep channels 3&4 of the H9000 running at +4dBu for optimal signal. I route the output of FX Chain 2 to hardware output 3&4 of the H9000, which I send out via DB25-TRS 3&4 to channels 11&12 Return loops of the RJM Effects Gizmo.
6. The loop outputs of channels 11&12 of the RJM Effects Gizmo go back to the amps's effects loop Return using TRS to XLR cables. Because the signals coming out of the H9000 are balanced, I use Radial Reamp boxes to convert low-impedance back to high-impedance signals, which the amps are more suited to. The Reamp boxes accept the XLR connectors and output signal through unbalanced cables that get connected to the amps' RETURN input.

Keep in mind that any disconnection of cables or muting of FX Chains will cut the signal because it closes the loop from the front of the amp through the effects loop. Because I'm only dealing with ONE pre and post loop, I leave them on all the time. If you need more than one H9000 FX Chain for pre, post, or both, you'll have to opt for the fully balanced version of the RJM Effects Gizmo, which would allow you to switch loops without closing the circuit, as if you had a loop switcher on a pedalboard.

Radial J48s require phantom power, so I use phantom power adapters in between wherever the use of J48s is noted. They are also not in the diagram. Why get so complicated? Because they sound amazing and are ultra quiet. Best of all, NO TONE SUCK! It feels and sounds 'same as cable' to me.

See the attachement for the wiring diagram.