pxeboot does not work on Sun X4540

Hello,

I'm trying to boot FreeBSD 8-CURRENT on a Sun X4540 (2xquad core 
Opteron, 64 GB memory, 48 SATA disks (in fact 47, the 48th is a write 
optimized SSD, because this box is a 7210 OpenStorage "appliance", 
running OpenSolaris) on LSI controllers, nvidia NIC) from our boot 
server without success.

The PXE on the NIC downloads pxeboot with TFTP, but then gets stuck at 
loading the kernel:
http://people.fsn.hu/~bra/freebsd/20090107-freebsd-x4540/Screenshot-6.png

pxeboot is configured to load the kernel via NFS (the default) and 
according to the tcpdump output, the client (X4540) issues an NFS 
GETPORT call and gets the response from the NFS server and then nothing 
else happens.

I've tried with LOADER_TFTP_SUPPORT=YES and the result is the same, the 
only difference is that the machine stops sending packets after the 
first TFTP read request (for /boot/boot.4th.split), which doesn't exist, 
so the server sends the answer and then nothing comes back from the 
X4540 box.

It seems that it gets to send exactly one packet, then freezes.

What else should be done to debug this problem?

Thanks,