Is the MIPU on the same network as the FXS? Is there any routers in-between the FXS and the MIPU?
I don't remember having any audio issues with an MIPU and a SIP device if they are on the same network.
You mentioned that it works OK on an MIPU 16, you tested the FXS on the MIPU 16.
Last question, since this is an MIPU24, did you install it like a PRI or T1 card, IE.., in slots S101, S103, S105, or S107 of the Base Cabinet or slots S_01, S_03, and S_05 of any Expansion Cabinet, and the next card slot (even number slots) left open?
