There’s loads of riding in the area, some marked, some on the OS map.
Try find a dyfi enduro map and add in a few bits off that if you do the climach-x too (don’t go over the field at the top though).
I didn’t think much of the mach 3 either although we got very lost (signs were all away for rerouting) and did an ace descent down past the golf course that I don’t think we should have been on! If you feel like a big jaunt then it’s fairly easy to link the mach 3 into the Syfydrin loop at nant too, just use an OS map to make the link.
I believe that they’re talking about making a mach 4 that’ll drop down the nant-y-moch reservoir anyways!