Any round-feed LNBF would work pretty well,
- give you maximum flexibility,
- maximum hardware choices,
- and be inexpensive.
Keeping the feed is very wise for the elliptical shaped dishes like the 84e, but may not be so serious for the round ones like you have.
Three choices come to mind, if you want to stay with the existing feedhorn.
- expensive Invacom QPF-031 (not to be confused with the QPH-031 which has a round feedhorn built in)
- Hughs LNB as shown in picture below (credit to Tron, I think)
- DishNetwork bandstacked LNB from SuperDish (credit for pix to Tron again)
There may be other options.