This is a good reference document to answer many wheel questions:
www.fastco.ca/web-content/Images/Wheels2006appguide.pdf It is from a wheel vendor (not sure if wholesale or retail), but besides showing which of their wheels fit which vehicles, it also has a listing of what the OE bolt pattern, offset and centre bore are, all important considerations.
On an AWD vehicle, I believe that the correct size is much more critical than with 2WD vehicles - differential or tranny damage could occur under certain circumstances.
Multi-fit wheels are generally what they call "lugcentric" versus most OE wheels being "hubcentric." That's where the centre bore measurement comes in. On a hubcentric setup, the wheel rests on the hub, and are held in place by the lug nuts. They are centred by the hubs. In a lugcentric setup, the centre bore is much bigger than the hub, so the wheel does not rest on the hub, and is held, supported and centred entirely by the lugs. This can cause vibrations, especially on some vehicles which are more prone. Another issue, which I feel is debatably, is whether or not the vehicle weight can be supported by the lugs alone, or need to be supported by the hubs and lugs.
On the issue of wheels, look for "take-offs" from other Subarus, available usually through wreckers, tire dealers and of course Morty's shop. These were, as the term implies, taken from other Subaru vehicles. Otherwise, if you can find new aftermarket wheels that are hubcentric (can be found with some homework, as long as they are made for your car), that is another option. Costco came up here before as being one of the few places selling aftermarket hubcentric wheels. In my case, I ended up with a set from them last winter for our '03 VW Golf. They were hubcentric - in fact, manufactured by Fumaglli, a huge OE supplier of wheels, and in this case, the OE supplier to VW. Only difference between the Costco purchased wheels and the full-sized spare wheel was that there was one less stamping - the VW logo. I also called Costco today to see if they have wheels for my new '06 Toyota Sienna. They do have a 16" Toyota specific wheel. Guess who's the OE supplier for the 16" Sienna steel wheels? Fumaglli. I suspect these will be also Fumaglli steels at Costco, but regardless, they are hubcentric to a number of Toyota fitments, and likely made by any one of the OE suppliers to Toyota. I would save over $30 per wheel for exactly the same as what I can get from a dealer.
Which leads me to believe that it should be no different for a Subaru. Call Costco. You will need someone knowledgeable on the other side, so a few calls to different locations may be needed.
As for your winter tires... Well, tell us a bit about where you drive and how you drive - lots of people here can help you narrow things down.
And lastly, welcome to the forum! Make yourself at home. We are a fun, but quirky bunch.
