Yes, you need an active splitter.
I've got the SH 2100 and the MMSI filtering answer isn't that simple on that unit.
Depending on firmware version (needs to be sent in for upgrade) it can be smart about ignoring your own target MMSI or not on the built in display.
feed from it will even with the latest firmware (upgraded in August) still send your MMSI target info, thus making It pretty useless.
I re-routed my plotter to take the AIS NMEA
feed from my Em-trak tranceiver.
I just want to point out that aside from this issue I've been super happy with both the SH product and their awesome support!