I didn’t know there was a wired version of the Fishman. hmm.
Well, the overarching issue in this choice is where the A/D conversion takes place. What comes off the guitar? The GK-3 sends parallel 6 analog signals, which can be turned into MIDI or not. It’s this conversion to MIDI that bothers me, so I avoid it. Roland’s version of the MIDI conversion is no doubt worse than Fishman’s anyway. That means the GP-10 is essentially a guitar processor that starts by converting analog audio to digital audio. Then it supplies a new guitar body (digital modelling), effects (digital modelling), and an amp (digital modelling). In this normal mode, it never knows or cares what MIDI note number or velocity may be involved.
The analog signal from the GK-3 will have noise in it. There are good noise suppressors in the GP-10, and you can adjust these and other parameters to get a very clean sound. Fret buzz is another issue, particularly on acoustic guitar simulations. We normally try to fix this at the source with neck and action adjustments. I’m pretty good at that kind of thing, but I found the exercise to be frustrating and not entirely successful. The installation of the GK-3 is non-trivial. I highly recommend using the screws to install the hex pickup because tiny adjustments can make a big difference in getting a loud enough signal and minimal cross-talk.
The fret buzz problem can be mostly addressed by tweaking certain details in the acoustic guitar setup, such as knocking down the EQ top end. The results are quite satisfying because acoustic guitars naturally reveal more fret buzz, and the top end that carries the fret buzz is unnatural anyway.
There’s an option to blend in the output of the normal guitar pickup, but I rarely do that. It’s great to have twelve electric guitars (all of which can become 12-string), 6 acoustic guitars (all of which can be converted to 12 string), a banjo, and a Coral electric sitar without having to buy, maintain, or store them. There are also bass and synth options, but these are less useful. I’d recommend a real bass guitar and keyboard-controlled soft synths for those sounds. There are some hex-pickup specific tricks that are nice, such as what happens when you apply distortion to each string before mixing them. (As opposed to what electric guitars normally do – the normal pickup is shared by all strings, thus creating a mix, which then hits the distortion.)
I prefer the GP-10 amp sims over stock Cubase guitar amp sims, particularly the Fender Bassman and the Vox AC-30. I once sent a non-guitar audio track through the GP-10 to see if I could just use it as an outboard amp sim, and it worked.
Another issue - The signal chain for effects has limitations. You can change the order of the effects, but you can’t do parallel effects or use the same effect twice. That would be asking a lot for the price. If I wanted to do these things, I’d have to (1) record the modeled guitar into Cubase, (2) build the effects chain using plugins within Cubase, (3) send the result back to the GP-10 after the performance was finished to pick up the amp model, (4) and record the result coming from the GP-10 before doing further production. This isn’t a workable solution because the final tracked sound wouldn’t match the sound during the take. To escape this problem, I’d skip the GP-10 amp sim in favor of a plugin amp sim in Cubase, at least during recording. Possibly swap it out for something similar (or better) on the GP-10 later.
Also, when you record trough the 6-track GP-10 ASIO driver, there’s only one stereo channel of audio coming from Cubase as a cue. This isn’t a problem, other than making the workflow a little bit more awkward than if you just took the stereo out from the GP-10 into your regular audio interface, as you would with a conventional instrument.