2" lift shouldn't be too hard on your CVs and shouldn't affect power delivery or transmission life. If you're going to drive the car 99% on the highway and occasionally take it on trails like this, just go 1.5". If 99% trail riding I would go 2.5".
215/75/15 is the biggest tire you'll be able to fit without some crazy spacers or wheels, they shouldn't rub too much with 1.5"+ lift. Supposedly the 08ish Forester struts have a little more clearance, pretty sure the 2000-2004 Outback front struts have more clearance, but still 215/75/15 is about as big as you can go.
As you mentioned your approach and departure angles will be much worse than a Jeep. At a minimum remove the plastic bumper covers or the trails will eventually remove them for you.
AGX struts are a little better than standard replacement struts and aren't too expensive. Beyond that they get expensive but ride and hold up better. Lift springs would be worth looking into, that would be a better way to lift it than spacers as it will get you higher off the bump stops at ride height.
Having done it, I would say it's not worth swapping to an H6 for mild trail riding. If you really want an H6 and obviously don't mind having an auto, I'd just buy an H6 Outback. With the five speed auto would be even better.
The biggest advantage that Jeep will have over your Subaru is gearing. I haven't seen this trail you're talking about so I don't know how steep it gets, but any long steep grade will probably be impossible in your Subaru (this is all relative, we've certainly climbed some things without low range a lot of people would consider long and steep). I haven't driven many of the automatic cars off pavement but mine is terrible, certainly no better than a five speed manual, you still need momentum to get up short steep hills. It does work better in 1 or 2 than D.
I wouldn't worry so much about ground clearance numbers. Worst case you scrape the bottom a few times, or a lot of times, it's steel and it's a 22 year old car, just make sure the oil pan and gas tank have good protection.