Been down this road (though it's been a while). For converting/playing back giga format, here are my recommendations:
1) Kontakt. Ain't cheap, but if you already have it, then it's a no-brainer. Does a decent job importing and playing back giga files.
2) G-player. A one-trick pony... Probably not worth its price if you don't have a substantial giga library, but if you do, this is the king. Probably the most accurate because it plays giga natively -- there's no converting. Another advantage is that it's still being developed and updated.
3) Samplelord. An older, multiformat player, and stopped development at 32 bit. Still, I used this for years before getting Kontakt. In terms of accurate playing, IMO it's second only to G-player. Sad it's not being developed anymore, because the dev really knew his stuff. (This player is also excellent at playing soundfonts).
4) Linuxsampler. Free, but rather complicated to figure out. I never tried this one, but other users have sworn by it. It's free, so if you have a small Giga library, and are tech-oriented, this one's definitely worth a try.
These all have demos, so you can try them out.