Not sure if this is it but did you install the USB driver for MOXF in your MBP? I had to install it to connect to my Motif XF by USB, I don't think its class compliant for plug and play. When you plug in via 5-pin MIDI through a midi/audio interface module, you don't need it.

USB Driver

I have not done this David. I will definitely give this a try and let you know. I guess I assumed it would be plug and play like most of my other midi controllers I've used. This makes sense though.
Thanks man!

I first had to install the USB driver to get XF to interface with Melas software tools on my MBP, then when I plugged in to connect with MS3 it worked fine. I'm going to bet this will fix it for you. but i'm not an expert so ... I know it won't hurt so no harm.

Hi David. Thank you so much for your help. The USB driver definitely worked. As soon as I plugged in my MOX it recognized it in MS3. The issue I am having now is getting Mainstage to now recognize the MOX when I'm assigning it.
I went into Utility > Switch > LocalCtrl and turned it off. But when I hit a key on the MOX it doesn't register as receiving anything in MS3, like my other controllers would do. So I'm not able to assign anything. I feel like there is setting on the MOX that I'm missing.
Would you mind walking me through your MOX settings to see where I'm short.

One thing that at least let's me know I'm on the right track. If I hit my DAW Remote button, I can scroll through the different MS3 patches via my 1-16 buttons on the right. So I at least know the MOX is talking to MS3.

Thanks again man. You're a lifesaver.

Sorry, I don't think I can help. (a) I don't have a MOXF (yet), I have a Motif XF7. I'm 1000 miles from expert on this topic, maybe someone else will jump in to help you. You could post over at the MOXF forum at motifator.com as well, there are helpful guys over there. BM is the resident expert but I think he's very busy of late with all of the new Montage users. understandable.

The issue I am having now is getting Mainstage to now recognize the MOX when I'm assigning it.

Sorry, you have everything you need on the MOX side of things and as you seem to know the issue you are having is with Mainstage. I don't know and can't really help with that product.

I know the light is bright over here, but like that old joke, you dropped your keys down the block... You're looking here because the street light is on... Is there a support site for Mainstage?

If you can meet me half way we may be able to shed some light down that dark alley that is getting Mainstage to work... Can you describe exactly what you have setup in Mainstage?

The driver (Yamaha Steinberg USB) allows your computer to recognize both MIDI and Audio coming from your MOX. It seems you have that working... The MOX setup is easy.

If the MIDI IN/OUT = USB on the MOX, you've done your part
Audio is automatically routed out via USB. either as a single or dual stereo output.

What are the setup options in Mainstage? Don't assume I know what it is, I'll help with the MOX, you work with the MainStage side of things. We'll try to help out. Let us know.

I've got a Mox8 that is seen on my macbook pro when I check the USB section, but is not seen by Mainstage 3 at all. Using a 2 keyboard setup (other a Korg), both keyboards will receive midi, but I cannot get the Mac to receive midi from the Mox. I cannot believe that people with the MoxF are still having the same problem. Is Yamaha too close to Steinberg to care about other companies? Since my Mox8 is a little dated, i was toying with the idea of upgrading to a moxf series, then I find out that people are still having the same problem getting it to work with Mainstage 3. I have no intention of buying another Yamaha until they fix their integration problems and write updated drivers for their older products.
On my end, i've tried installing just about every version midi driver yamaha has to no avail. I've uninstalled and reinstalled. Barring any help from this forum, i'm going to sadly ditch my Yamaha and steer clear of them in the future.

In order for your computer to properly recognize the MOX8 you need to download and install the Yamaha Steinberg USB driver that is appropriate for your particular computer's operating system. There are literally hundreds of users successfully using Yamaha synthesizers with Mainstage. We can give you detailed help with setting up your MOX, but when it comes to specifics about another manufacturer's software we can be of some help but will need to refer you to the included documentation or to the manufacturer of that product when it comes to customizing your setup with their software. We simply cannot take you but so far beyond the basics of setting up.

MainStage configuration Here is a short article that maybe helpful, although written for the MONTAGE, your MOX uses the same Yamaha Steinberg USB Driver.

If you get stuck post your questions in a new thread. Not one where obviously the original poster couldn't get it working. The title is supposed to be their question... it is certainly not a statement of fact... because the keyboard does work with MainStage!

Yes the Drive solves the connection, neverthless a new issue im having is that when i connect the plug of intrument (to mix with yamaha voices) an interference noise comes thru, i have to turn down the volume of instrument at the interface , sadly not being able to mix both sounds (mainstage and yamaha's)

There may be an impedance mismatch with the connected instrument or an issue with the cable (shielded vs not - quality - etc).

Length of the cable also makes a difference. The shorter the better.