i found the esi gigaport hd for around 150 €. this is a good price for 8
output channels. but i think it wont run under linux.
ESI Gigaport AG runs perfectly under linux using alsa's snd_usb driver.
i see no reason for HD version to be not supported, as core seems to be
quite the same.
also, actually, AG works even better in linux than in windows, because
in linux you have all channels available and separately addressable out
of the box, while in windows you have to do some driver switching
procedure and rebooting to toggle between 8ch and stereo mode.