A lot of people express concerns over keeping plecs with discus but very few ever say anything about keeping them with angels. To be honest though, I don't think there's any real danger with keeping them with larger flat-bodied fish like angels. I've never seen a plec suck on a discus (or angel) and don't know anyone who has either. I suspect this is just a one-off occurance and would expect that a plec that has a stable diet won't go after angels' slime coats. I have kept smaller plecs such as bristlenoses with angels and never encountered problems. Having said that, perhaps someone will come along who has first-hand experience in this sort of mix going wrong or maybe you simply don't want to risk it. Besides that, the plec will need an even larger tank so I personaly think you should get the right size tank for it so you don't need to keep moving it around.