Once Yamaha kill something off it is seldom that it is ever resurrected, so the XG synth is probably gone for good.

Don’t forget Yamaha now own Steinberg (The inventors of the VST and low latency ASIO drivers) therefore might I suggest you have a look at Halion Sonic as it has a high quality GM2 sound set (According to the details available and which is probably as close as you’re going to get to XG for the foreseeable future) and all the new voices that have been added (Since it replaced Hypersonic) were designed and programmed by the Motif programmers, so should be ideal for use with Yamaha products.

Something worth looking at

Bill