HdspLoader and HdspMixer are two programs that will intereact with the RME devices: the first provides the firmware it needs to run, the second interacts with the device just like amixer, only provides a sane GUI :D

Basically, since the RME has a routing matrix built-in, using amixer will provide every single control, which will be a totally horrible way to work. Since HdspMixer provides a good way to interact with the sub-mixes, its advised ;)

HTH, -Harry

PS: I have a Multiface 2, so my experience might be slightly different to yours with the AIO.