Probably a stupid question but why do you need an fx loop in an attenuator?
If you have an amp without a loop (which the amps that need attenuators usually don't have, Plexis, JTMs, etc), then this is a great, non-invasive way to be able to run W/D.
I think I understand the concept now. The HO attenuator works like the UltimateAttenuator, by reamping the attenuated signal with a built in amplifier. So on this special one, there are two of these amps in the HO, one for Wet, one for Dry I think. Running on 2 cabs you will have a great sound, if you run a fully cranked Plexi in front and listen on TV volume through two 1x12 cabs - one dry, one wet, for example.