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Obviously I would like the best sound out of BIAB for the least amount of expense.



To be honest with you, the best sounds out of BIAB are the RealTracks. No synth is going to beat those for realism.

But, if that is not meeting your needs or you must have a synth, the SD2 sounds really good and is fairly priced. For software synths, I would also check out Vi.One, which is running for about $100 at some places. It has GM and other instruments. (Check the system requirements!) Sampletank also looks good at $200. If you buy it in the next month, you can also get the Miroslav Philharmonik plugin for FREE! While it requires some skill, it's apparently an excellent plugin for those type of sounds. Guitar Center also has a 10% off sale, so that's even more savings.

Still, you're better off having a real player and RealTracks gives you that. If you need to upgrade to get them, I would suggest that over any synth. I can certainly vouch for the guitars - they're really good.