i did the obvious, got the Purist. should have spent the few bucks for the HD. i've done the HEXFREDS (courtesy of Doc), then the BlackGates (my own self). each change was not subtle, as they say at Stereophile. bass really is much better with these changes. i hadn't soldered in 20 years when i installed the HEXFRED board. a 40 watt iron is a must; that and taking the time to plan out how you're going to proceed. this was important for the BlackGates, since they are considerably larger than the standards, and are just lugged, so have to be wired first. and since they a tad heavy, i opted for 18 gauge solid for mechanical stability.
just get the HD.