The Helixnet documentation available online indicates that up to three Main Stations can be linked via IP and / or fiber. In such a system, with three Main Stations linked, Q1. are all three program audio inputs available via the network, for assignment to any of the 12 available channels? Or only a single program input? 
Q2. Are program inputs from Remote Stations (connected either via party--line or IP) made available via the network in any fashion for listening, or are those inputs local to the station only? 
A1. Only one PGM can be assigned per channel. With 3 linked systems the PGM from each Helixnet basestation can be assigned to a different channel. You cannot assign 2 PGMs to the same channel
one pgm is connected to 1st Mainstation and another pgm is connected to a remote station..... 
at a station (BP for example) you can only assign one pgm to a channel (example PGM from the Mainstation) if you reassign the the other PGM from the remote station..... the channel will drop the first PGM assigned to that channel, and assign the "Newly Assigned PGM" to that channel and the first assigned PGM will disappear from that channel you can only have one Program signal assigned to a channel at one time
A2. The 4wire / PGM input on a Remote Helixnet station can be made available system wide