You can w/ the Intellifex, but not so much w/ the SPX 90 though there are short cut/cheats to sort of get there, ex. Hall Reverb and play w/ the predelay time -- set to say 250mS-- to have delay and reverb.
used the spx90, and rev7 for years in a PA rack, and owned a few intellifexes
zachman nailed it--the spx is a very dated piece of gear and it's simplicity is it's greatest asset-the fex is a better sounding overall gtr rack unit.
i use the spx-2000 nowadays and it has 3 modes, preset, which uses the latest in yamaha rev-x sounds, classic, which emulates the old spx series, and user, which are user modified preset slots. usb port for computer editing, word clocking, aes/ebu...nice updated features
I own one (cost me $25) and I love the pitch shifting and the Symphonic preset for guitar. It needs to be in a mixer/parallel or in a w/d or w/d/w config but it does sound killer. If I had the space in the rack, I would definitely be using it!