The book is not that expensive and definitely worth the money, IMO. There are three parts: intro to subtractive synthesis, sound analysis, and recipes. By sound analysis, I mean he spends a lot of time explaining how to figure out what wave types (saw, square, etc.) and in what combinations you need to come up with a synthetic version of an acoustic sound. The second section is dry and heavy going, but the book is worth it just for the first and third.
I spent some time "cooking" many of the recipes on DIVA. I first did some calibrations of envelope parameters (tedious, but necessary). That's straightforward using SONAR. I did not use Welsh's recommended way of getting filter cutoffs. A much easier way is to set the filter resonance all the way up, set the filter at the position you want to measure, play a bunch of adjacent notes low on the KB (playing through a saw wave), and look at the result in Span. The cutoff jumps right out at you, or at least until your cutoff settings dip below maybe 500Hz.
Some of the cooked recipes are terrific sounding and some are kind of lame. The pads and leads are nothing to get excited about IMO. The acoustic synthetic sounds are a mixed bag, but some of them are *very* good indeed. Of course, the same recipes on a different synth may be a whole different thing.
By the way, I posted the DIVA patch library for free download, if there are any DIVA owners out there interested.