Hi spiegeljb,
I think you may need to ask around in the citrix forums. If your hardware can support IOMMU either in AMD forgot what the name of it is or Intel VT-d, you can directly pass pci to the HVM. Then the HVM will install the proper drivers rather than using pv-drivers or emulated IO drivers. Remember if you don't have IOMMU in your BIOS you will not be able to do pci pass thru to HVM. Below is an example of my pfsense config file :-
import os, re
arch = os.uname()[4]
kernel = "/usr/lib64/xen-4.0/boot/hvmloader"
builder='hvm'
memory = 1024
shadow_memory = 8
name = "pfsense"
vif = [ 'type=ioemu, mac=00:16:3e:xx:xx:xx, bridge=eth0, model=e1000',
'type=ioemu, mac=00:16:3e:xx:xx:xx, bridge=eth1, model=e1000',
'type=ioemu, mac=00:16:3e:xx:xx:xx, bridge=dummy0, model=e1000',
]
disk = [ 'phy:/dev/vgvolume/pfsense,xvda,w' ]
, 'file:/home/pfSense-1.2.3-RELEASE-LiveCD-Installer.iso,xvdc:cdrom,r' ]
device_model = '/usr/lib64/xen-4.0/bin/qemu-dm'
boot on floppy (a), hard disk © or CD-ROM (d)
default: hard disk, cd-rom, floppy
boot="dc"
vcpus=2
cpus=["1", "2"]
pae=0
acpi=1
apic=1
sdl=0
vnc=1
vnclisten="0.0.0.0"
vncconsole=1
vncpasswd=''
stdvga=0
serial='pty'
usb=1
usbdevice='mouse'
on_poweroff = 'destroy'
on_reboot = 'restart'
on_crash = 'restart'
Hope this helps
Eric