Well, we know that wheatens are typically aggressive and territorial. However, their playful nature is actually very similar to that of the feline variety. I would say that the soft coated wheaten terrier should actually play along quite well with a cat. However, I would warn you that a well established wheaten may be less receptive the the arrival of a new feline bundle of joy than would a younger wheaten.
Cats by nature are less territorial and although initially frightened or appalled by the addition of a wheaten terrier to their space, should warm up quickly.
In either case, the first encounter is paramount. You want to make sure that the wheaten and the cat have a pleasurable first interaction. To do this you want to keep your wheaten leashed and your cat in the arms of an individual with whom he or she is comfortable. Slowly bring them together and let them smell eachother. Animals loveeeee to sniff. Once they have proven they can interact while constrained in a civilized manner you can put them on the floor together and under a watchful eye let them play. The wheaten will be stronger than the cat, but the cat will be quicker and meaner if instigated. If they begin to get noticeably angry at one another separate them and try the sequence again later.
There is really no reason that cats and dogs can’t live peacefully together. Just give it a shot. I think you’ll be pleasantly surprised by the outcome.