exxos's Atari, Amiga & retro forum

I am in the process of backing up all my stuff from disk via my Falcon and STFM and placing on a PC GemDOS drive or MSA archive file under STeeM.
One of my old programs I came across I recovered from disk, and still compiles under GenST, but it requires the use of the MasterSound cartridge to read an input signal from the sound recorder cartridge. I no longer have the real hardware so I can not run this on the real device anymore so I am looking towards emulation on a PC to replicate the setup for this program. I see STeeM is able to run cartridge Roms, but I have not found any such cartridge .STC file for mastersound as yet. However STeeM does come supplied with a Replay16 ROM, and I can attach and emulate an STFM with this cartridge enabled.
I am wondering in assembly, how can I read the input signal from this device, and secondly, under an Emulator, how do I bring an input source to the virtual Replay cartridge input source running under STeeM? I assume it can be done, otherwise why ship STeeM with such a ROM. I have downloaded the Replay16 software and clicked Monitor but I see no signal from my PC audio stream being default streamed into the virtual Replay cartridge.
The instructions for the cartridge stuff in STeeM is quite limited.
Anyone got any experience on this?

All that steem (or any other emulator) does, is to read that cartridge ROM, and make it available at memory location $FA0000. So as a first step, you need a dump of that ROM image. If that cartridge originally was connected to some hardware, then you also have to emulate that hardware somehow.

I don't think Master Sound has any ROM on the cartridge.