xen 4.1.2 not booting on Linux Mint 13 Maya with grub2 1.99 UEFI boot

1) Linux Mint 13 Maya with 3.2.0-26-generic kernel and latest updates (except those that were withheld from updating)
Xen 4.1.2 package installed via synaptic

Hardware: Asus Sabertooth X79 motherboard, i7 3930K CPU with VT-d support (C2 stepping), 32GB memory, 120GB SSD and several WD20EARX HDDs, PNY (Nvidia) Quadro 600 GPU.

Linux Mint 13 is installed on the GPT partitioned SSD using the following partitions:
/dev/sda1 EFI system partition (fat32)
/dev/sda2 /boot partition (ext2)
/dev/sda3 formatted to LVM:
/dev/mapper/lm13-root / partition (ext4)
/dev/mapper/lm13-home /home (ext4)

UEFI boot.

Linux Mint 13 boots just fine and mounts the LVs (/ and /home).

2) Installed xen-amd64 (Xen 4.1.2) and auxiliary packages via synaptic and ran update-grub. Rebooted and the system stopped at this screen:

(XEN) Xen version 4.1.2 (Ubuntu 4.1.2-Zubuntu2.1) (<email address hidden>) (gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5) ) Mon Jun 18 14:13:52 UTC 2012
(XEN) Bootloader: GRUB 1.99-21ubuntu3.1
(XEN) Command line: placeholder
(XEN) Video information:
(XEN) VGA is text mode 80x25, font 8x16
(XEN) VBE/DDC methods: V2; EDID transfer time: 1 seconds
(XEN) Disc information:
(XEN) Found 0 MBR signatures
(XEN) Found 0 EDD information structures
(XEN) Xen-e801 RAM map:
(XEN) 0000000000000000 - 000000000009d400 (usable)
(XEN) 0000000000100000 - 00000000deb00000 (usable)
(XEN) System RAM: 3562MB (3648116kB)

3) The system doesn't respond to keyboard input and needs a hard reset (power off) to shutdown/reboot.

Here is the relevant part of the grub.cfg file:

### BEGIN /etc/grub.d/20_linux_xen ###
submenu "Xen 4.1-amd64" {
menuentry 'LinuxMint GNU/Linux, with Xen 4.1-amd64 and Linux 3.2.0-26-generic' --class linuxmint --class gnu-linux --class gnu --class os --class xen {
   insmod part_gpt
   insmod ext2
   set root='(hd0,gpt2)'
   search --no-floppy --fs-uuid --set=root d461c2c7-e72c-47eb-b09d-3270382d295c #remark: /dev/sda2 /boot partition (ext2)
   echo 'Loading Xen 4.1-amd64 ...'
   multiboot /xen-4.1-amd64.gz placeholder
   echo 'Loading Linux 3.2.0-26-generic ...'
   module /vmlinuz-3.2.0-26-generic placeholder root=/dev/mapper/lm13-root ro quiet splash
   echo 'Loading initial ramdisk ...'
   module /initrd.img-3.2.0-26-generic
}

Adding
   recordfail
   gfxmode $linux_gfx_mode
   insmod gzio
above the insmod part_gpt produces this screen output BEFORE the above screen appears:

"Booting a command list

Loading Xen 4.1-amd64 ...
WARNING: no console will be available to OSLoading Linux 3.2.0-26-generic ...
Loading initial ramdisk ..."

4) About 2 months ago I installed Linux Mint LMDE and then the Xen kernel and it booted just fine, using the same synaptic installation procedure with no modifications.

I was hoping that the Xen hypervisor (dom0) using a LM13 Maya installation would work the same way and boot.

5) I completely removed all xen packages and re-installed Xen. No difference - it doesn't boot!

I also tried some grub commands for the xen kernel (limiting or increasing the default memory size to 4GB, for example), but that made no difference.

I suspect that either the xen-am64 kernel doesn't work, or perhaps a problem with the initrd.img-3.2.0-26-generic ramdisk. The same ramdisk works with the regular (non-Xen) LM13, though.

I understand that initrd.img-3.2.0-26-generic is updated with the update-grub command, for example to include the LVM2 module that is needed to access the / and /home partitions mounted as LVs?

I'm still searching the log files but there seems to be no entry of the xen boot, compared to tons of logs for a regular boot.