Using 2 different soundcards aggregated together with ASIO like you specify, each soundcard will have a different latency. So cueing up in your headphones (referencing one ear against master output) you may have it matched up sounding ok, but then when you bring the volume up on the track you've been cueing up, it won't actually be in time. Also yes, no volume faders on the X1. I guess you could map the faders on the F1 to your channels, but the mappings are going to get messy and confusing pretty quickly