I really like what you've done here, it really changes my mood. The Pedal point really fills it up. The trouble with using pedal point tones though is that it restricts you from using certain chords effectively. Think of that pitch as the root of your chord, a nice number of notes within the given 12 will go with it. However it also leaves a great deal of pitches that will cause dissonance making it sound unclear.
I think that if you keep the pedal point then you should try moving other lower string instruments up in their range or omit them. some intervals may sound bad in a certain configuration. Simply moving dissonant pitchs(grating notes) up an octave will clear it up.
You have quite excellent material here. Really all I think it would take is letting that Drone pitch handle the bass and the perc keep the motor going so that the listener can keep with the piece. The higher ranged string parts are doing well as they are.