Does Blue Iris have the ability to synchronize the archive to a remote server ?
if so, where can I find it to test ?

For sub-streams to be used efficiently, make sure 'direct-to-disk' recording is enabled in BI and that they are correctly detected in BI's camera settings. This should accomplish everything that it says it will, including providing both RTSP streams as specified in the cameras themselves and removing any extra encoding that isn't being produced by the camera itself—unless the BI configuration is altered in some other way, of course. Here, "direct-to-disk" is crucial and, if it hasn't been turned on, should significantly lower your CPU burden.

Well that's off topic