Hello Martin,
"ASIO Directo Monitoring" can only be enabled if the soundcard supports it. I haven't used the Echo Mia, but it is one of the better ones on the market, so I don't see why it wouldn't. In Cubase, make sure that you've selected the Echo Mia ASIO driver (whatever it's called) rather than the Cubase generic "ASIO multimedia driver" or something like that... haven't used 5.1 in quite a while. Also, check to see if there are new drivers for the Echo Mia. The other problem sounds odd... make sure that the audio inputs are selected correctly for the channels. Also, keep in mind that in Cubase VST 5.x all stereo channels are "Odd numbers" because the Left channel is set to the odd numbers and the Right channel to the even.