I've ordered and tested prototypes for the Modified Linkwitz crossfeed board. I'm not doing final boards through ExpressPCB as I have for all my other boards, which should make the final boards cheaper than if I'd got them through ExpressPCB, but it means more work to get boards ordered. I'm still in the process of learning how to make proper Gerber and drill files, and choosing board houses, getting quotes, etc. I hope to get this ball rolling in the next day or so, which would mean that final boards could be here in as little as 2 weeks. Plan on waiting 3 weeks, though. I'll post an ad in Mall-Fi when final boards are ready.
On the Meier crossfeed, it simply won't work right if it isn't buffered. You'd think that a simple fix for this problem would be to sandwich the crossfeed circuit in between the META42 board and a pair of EL2001s, but that doesn't work for some reason I never figured out. My vague recollection was that there was some kind of stability problem. I got frustrated fighting with this and gave up on it months ago. That's the main reason I use the Linkwitz crossfeed -- it works well with the META42 board, without fuss. The other reason I like it is that it's simpler than the Meier crossfeed -- fewer caps, and the switching setup is simpler, too. The sound agrees with my ears, so I haven't looked farther.
Apparently Jan Meier's new Porta Corda 2 uses a different crossfeed design which doesn't require buffering, which lets him remove 2 of the LM6171s from the design. Too bad he's not sharing designs any more....