The other PBS station you are getting is probably VPT (Vermont Public Television) (WETK). It is an occasional visitor to Orleans, and you seem to have good elevation to be successfully pulling in WWTI!
If you are getting WWTI, you should be able to pull in WWNY (RF 7) with the right setup which will get you CBS and FOX. The CM4228 seems to be weak on VHF stations which is probably the reason you didn't get WWNY. If you don't mind waiting, there is a repeater coming up soon from the same tower as WNPI-DT. It's a fair bit weaker, but if you have decent reception of WNPI at all times, it might be usable for you.
Macroblocking on the OMNI's doesn't surprise me. You're in the same reception shed I'm in where the Herbert's Corners tower doesn't like to penetrate. Those channels desperately need a power boost, imo (City-DT is from the same tower, and comes in perfectly, something is just fishy with the omni stations) Maybe they're lower on the tower? They are supposed to have more ERP than City, but it doesn't look like it from here.