I like the Apex on the Duos a lot, they really make things more lifelike and natural. They are the same on the amp stands. If you were only going to get the apex or the F1 carbon fibre shelf, go for the apex. They just about doubled the gain the stand itself makes. With the 88s the F1 shelf works real well, with some brighter sounding gear it could be to much.
Also you can get away with only one amp stand for the 88s, I had that originally and was blown away at the improvment. I eventually got a stand each for the 88s and it does improve it over sharing a stand. If it was down to a choice between one stand with apex and F1 shelf I would go for that over 2 stock stands, of course if you can afford two tricked out stands your gonna love it thats for sure.