Hi Takashi, hi Florian,
I found a similar MIDI crashing bug on a dual Opteron machine in 2005, even with only one processor installed, which I reported at the time on alsa-devel. The card was an M-Audio Audiophile 24/96, normally reliable.
I couldn't replicate this problem on an Asus single processor Opteron board, so I concluded it was a quirk of my dual socket Tyan S2875 motherboard:
http://article.gmane.org/gmane.linux.alsa.devel/24682/ http://article.gmane.org/gmane.linux.alsa.devel/25323/
Last time I tested it, earlier this year I think, the bug was still there. I even flashed the BIOS of the Tyan board in case it was a BIOS bug, but it made no difference. I installed a 32-bit distro and that made no difference either.
Maybe there is something more generally wrong here, which only affects dual-processor AMD64 hardware. I can make the Tyan machine available over SSH if that helps, it has a fixed IP address.
Cheers!
Daniel