You can add as many IPTV sources as you want in NextPVR - just hit the Import button to add another.
Unless I'm doing something wrong it doesn't work the way we would want it to work.
For example M3U source1 is limited to 3 connections so we import that whole list and flag it as 3 connections.
Then we import M3U source2 which has a limit of 5 connections.
Same with M3U source 3 with another 5 connections.
Since these could all be from different services the stream counts are unique to each M3U file.
However after importing them all it would be nice to be able to set priorities on each provider and then group all similar channels from OTA, Cable and all M3U sources.
Right now it just appears as one big M3U list without a way to monitor stream usage which is the main issue. Each M3U list should work very similar to adding an HDHomeRun prime that gives you 3 additional tuners. Then add a Quatro and get 4 tuners but with different channels, etc.