Visit another website, xt6.com. Huck369 is a site moderator and the first person to do the auto to manual conversion. He still has the car and has a wealth of SVX knowledge. He may know the onboard procedure involved in pulling the transmission trouble codes.
If the transmission is shifting through all gears but with no power being transmitted to the front differential, than maybe the problem is the front differential. A transmission from an early Legacy will bolt to the ER33 engine, but I have to believe it is less strong than the SVX version. The SVX has a history of transmission and rear axle bearing failures around
125K miles. The car is just too heavy and powerful for these two components.
You really need to find the code pulling procedure. But no matter what the problem, this fix is probably going to get pretty costly.