Hi Amy, let's try to clarify what you're trying to do here. First I'm assuming when you say EX Keys you're talking about the softsynth from Toontrack.

Second, when you say you want to use a software replacement and have it play out to the Casio...you have it backwards. Your Casio is a controller that is playing the software EZ Keys that is IN your computer so the Casio is sending midi OUT to the computer (NOT audio), the computer is generating the sound using EZ Keys. You use your audio outputs from the computer, the audio outs of the Casio are irrelevant.

Here's how all this works. The casio has a USB midi out. You take a USB cable and plug it from the Casio to your computer using any of your computers USB ports. The computer should now recognize the Casio by displaying the "Windows has found new hardware" window. You shouldn't have to do anything, now the Casio is recognized. That's step 1. Step 2 is to open your DAW, since this is PG's forum, I'll use Real Band. RB is known as a DAW or sequencer. EZ Keys is a plug in that requires a host or DAW. It might work without a DAW (in Standalone mode) but I'm not seeing that in the advertising but it could be there. Once EZ Keys is installed, RB should find it. That process can be a bit tricky, lets leave that for later if there's a problem.

Here's where the confusing part is. First is the computer a new powerful PC or is it a typical donated antique thing? If it's old and slow, this may not work. If it's newer and fairly powerful it'll work fine. Next is the interface. If you don't have a separate interface and you're just using the PC's internal soundcard you'll get unacceptable latency when you try to play the keyboard. Latency is a delay you hear when you hit a key. You hit the key and a half second later you hear the sound. You'll come screaming back here yelling I can't play this!! Help!! You need a good interface that has a good ASIO driver. Again, I'm not going into details about that right now, just look it up. ASIO will reduce the delay down to the point you won't notice it. A good interface will also have good audio output plugs and a good software mixer. Run the audio out from the interface to your house PA and you're good to go.

Final point going back to the top. In this scenario the Casio is merely a controller that is controlling whatever software synth you have selected inside whatever DAW you are running inside your computer. The internal sounds of the Casio and some possible conflict with general midi have nothing to do with it. You make sure the Casio is set to the same midi channel as your EZ Keys and everything will be fine.

Bob

Biab/RB latest build, Win 11 Pro, Ryzen 5 5600 G, 512 Gig SSD, 16 Gigs Ram, Steinberg UR22 MkII, Roland Sonic Cell, Kurzweil PC3, Hammond SK1, Korg PA3XPro, Garritan JABB, Hypercanvas, Sampletank 3, more.