Hello, Sorry, I’m not fully understanding what the setup you are proposing is. Why are you suggesting using a Y-splitter cable? The DSUB connections on the H9000 give you 8 mono channels, 1 channel per each of the 8 cables on the DSUB snake. When making a connection with the DSUB cable, you should use a single cable to connect to a mono device, or a pair of the cables to connect to a stereo device. The only time a splitter should be used is if your device has a TRS jack that supports a stereo signal or insert path.
The EMU Proteus 2000 does in fact have sub outs which act as insert points as soon as the TRS end of the TRS to 2x mono cable is connected. I was going to connect the TRS end to the insert point of the EMU, whilst the send and return would be connected to the DSUBs of the H9000, one for send, one for return. See attached image of the send/return cable of the EMU Proteus 2000 and it’s sub out signal paths
