Presumably you could use the UX1 Line inputs to receive the HD300 outputs for your guitar processing. Set the HD300 outputs to Studio Mode. Then you could use the two UX1 inputs for your bass (guitar input) and vocals (Mic input).
here is a good place to start if you want a hardware solution: http://tascam.com/applications/recording/mtr_digital_portastudio/
but if you need more inputs... the UX1 will simply wont work for you....
if you need a hardware interface with more inputs here is another good place to start:
if you are simply trying to do this with what you already have... it isn't going to happen i'm afraid...
you can only use one interface at a time and neither of your devices have enough inputs.