I always like to throw the backup point out there, but thankfully I've yet to have a filter fail *Knock on wood*.
I'm going to assume your tank is a standard 90 gallon, which is the same footprint as my 75 gallon, just a bit taller. I have one XP3 on each corner of the tank. Like I already said, not only does this help get me extra water flow and keeping gunk from building up anywhere, which any old power head could do, I'm using two filters so any gunk that does get kicked up gets sucked up and out of the tank. I also spent a little extra coin for a custom water intake/return plumbling set. On one of the filters I have a spray bar about 12" long that's under the water pointing twords the front of the tank, and on the other end I have one of those jet nozzles with a venturi valve pointed at a 45 degree angle from the corner as well as a flat nozzle that I can aim where I want too. Again, this just helps me in keeping everything as clean as I can with all the driftwood in the tank. I only have one corner that collects gunk by design that's easy to get too with a python vac to suck out the debris.
I also have two different maintenance schedules for each filter so that neither one gets cleaned within 1.5 months of each other. If I really wanted too I could just tank one entire filter out back and lay a pressure washer to everything to clean it off and not have to worry much about the loss of bacteria because of the other filter that's running.
I'm the first to admit, I tend to take things a little overboard sometimes.
However I know how messy a single oscar can be, and I can tell you that with two large filters it's been easy keeping them both in top condition under a heavy load. So with two adult O's, and one large filter you may end up be cleaning it rather often, where as with two the load is split up between them. Meaning less work for you, but the fish are just as happy and healthy and the water just as clean.
You also mentioned the bio media, the XP's come with large baskets that you can do with as you please. The XP3's have 3 baskets, and I reckon the XP4's would have 4. It's easy to shove what ever type of media you want too in these things. I use bio balls and ceramic media in mine.