I just received a box from GR-Research of upgraded components for my old crossovers. Danny looked at the old parts, measured the values of the inductors, and supplied me with new air-core inductors, new capacitors, and told me that the resistors were good enough to use again. He was very cost vs. quality conscious picking the parts. He could have measured the response and designed new crossovers, but it wasn't worth the cost, including shipping a speaker, to me.
When I get everything installed in one speaker I'll do a comparison and post the results.
Danny's web site is a bit out of date. He as three new monitor speakers using the
Bohlender Graebener Neo3PDR planar tweeter, and will upgrade his existing monitors with this tweeter. Also, he has his own driver and custom amp for the
Rythmik Audio servo subwoofers.