As already stated, you cannot implement view 3 under one subscription with any of the older decoders.
Assuming you are prepared to run the third decoder on a separate subscription, THEN:
A. One of the ways to increase the number of decoders used (old ones) is to replace the existing quad LNB with an 8-way LNB. (Assuming you are prepared to run the third decoder on a separate subscription.
B. The older LMX 500 SLNB will allow for the installation of a 2 tuner decoder connected to the Legacy ports, which will be independent of the other decoders in the mix.
The Pace 2P PVR allows for the adjustment of the user bands so you could possibly come up with a configuration to support 3 of them on a SLNB (new or old).
You need to review remote control of decoders and which decoders you want to be able to view where, as this will affect how you distribute RH and HB to the two decoders connected under XV.
Easyview, UEC 4T HD PVR, SD PVR, XV
Spare decoders: SD PVR(2), PACE HD PVR 4T, DSD 660, 1110, 1131, Explora
2 unmentionable FTA decoders
Win 10 Pro (64-bit) build 1607, version 14393.351
1.2m antenna, 8-way universal LNB, 2x6 MS, FSM permanently connected.