I have the same problem.. Promaster 525C with benro S2 for spotter or standup glassing, Sirui T-0025x with OD micro pan head for ultralight backpack setup. Current issue with this setup:
1. Need to change the adapter plate mounted on spotter or bino adapter if you want to switch tripods
2. Benro S2 head does not work with Leica Stabilite Adapter (no stud for Geovids). The handle and adapter securement knob hit the Stabilite platform
It's probably going to end up costing me the price of a standard OD pan head to be able to swap back and forth.
I'm a less than polished spotter but my more specific take is this - my OD micro panhead is incrementally better than the ball head that came with my Promaster 525C. The basic benefit is being able to grid an area a little easier with the pan head and maybe a few ounce weight savings. Compared to the micro, my benro S2 pans smoother but doesn't lock down as precisely. You should be able to find a Tripod that comes with a ball head and use the field optics adapter and still have a very solid system for significantly cheaper than adding a Outdoorsman pan head and adapter. You can upgrade later as you see fit.
I bought the 525C from CameralandNY on sale 25% off ($225 shipped) and got the Benro for $50 or 60 on the classifieds. That's a pretty good system for under $300 and worth it over going for cheaper stuff IMO.