The Tilt can handle more than 3 connections simultaneously - but they have to share available bandwidth.
Things like the watch, ICS and standard mono headset are relatively low bandwidth and buffered and can be used together, transmit things in turns, one waiting while the other transmits etc.
A2DP however is realtime and high-banwidth, so it pretty much needs to be used alone, it won't like sharing the bluetooth hardware with other things.
One thing you can try is instead of connecting the A2DP headset to the Tilt, connect it to the PC, and play music on the PC. Depending on the PC's BT hardware/software it might work well there.
Samsung Galaxy S3 32GB
Revolution HD V11