armgr.exe stops the PC from sleeping if *any* receivers are powered up. If all receivers are powered down (power off or the usual soft-off state), it should allow the PC to sleep.
If the HPNA card does WOL (or the ethernet card that is serving the receivers, for that matter), turning a receiver on will force the PC to wake up - this was tested back in 2000. One thing though: a hard-off receiver will not wake the PC when you turn it on, only a soft-off one (ie, powered off with the power button, then powered on with the power button) otherwise it doesn't know the MAC address of the PC to wake it up.
I can believe that not all HPNA cards have WOL wired to anything useful, though
Hugo