With good hardware and a stable system you should be able to get the harware latency down to 2-5 ms. Then everybody needs a very stable and fast internet connec

With good hardware and a stable system you should be able to get the harware latency down to 2-5 ms. Then everybody needs a very stable and fast internet connection with low jitter, so you get average ping times of 20 ms or less. On top of that you have a jitter buffer latency of maybe 20 ms or less. (If you're very far apart geographically, you also need to consider the speed of light for the network transmission.) Under ideal circumstances you may end up with a total end-to-end latency of 30 ms. This is the same latency you get when standing 10 meters apart on a large stage. You probably won't be able to play bebop or technical death metal, but pop ballads or stoner rock should be feasable :)