DSLC-2/MSLC-2 and successors DSLC-2XT/MSLC-2XT are doing load sharing via Ethernet lines.
If you want to do load sharing between old DSLC-2/MSLC-2 and new DSLC-2XT/MSLC-2XT you have to make sure that latrest firmware Revision L is loaded in your DSLC-2/MSLC-2.
Latest DSLC-2/MSLC2 Firmware Revison L (partnumbers 8440-1877/-1878/-1977/-1978 can be downloaded here: https://wss.woodward.com/manuals/Support/Firmware_DSLC-2__MSLC-2