Triclo isn't registered for either paspalum or couch, but as you say it does kill kikuyu and there are some similarities between those species.

You're going to have to try a small area and give it a couple of weeks to evaluate, before you try a larger area.  I have seen a couple of anecdotal references to triclopyr (i.e. Triclo) being effective against both kikuyu and paspalum at the equivalent of 2L/Ha, so that sounds promising.  If results aren't pleasing, however, then the only product I know that does for sure selectively kill paspalum in lawns is called MSMA.  But it's very hazardous to use, and only registered contractors can buy and apply the stuff.  The larger lawn care companies will be able to offer this service, but let's hope that you don't have to do that, and that Triclo will work for you.

As for the couch, the only herbicide that I know for sure will kill it is glyphosate, which is of course no good for you due to damaging your other grasses.  So I suspect that Triclo is worth a try, as the most likely selective option.

Having said all that, I should say that triclopyr is one of the actives in GrassMate, although at a much lesser strength than it's present in Triclo.  So if GrassMate is having no effect, then it's possible that the Triclo may struggle as well.

Sorry I can't be more help.  I'm afraid that I'm no lawn care expert!  But I have cross-checked my suggestions with the information published on couch and paspalum by Massey University, and what they say is in agreement with my advice.