I want my metronome from cubase le 5 to play back through my tascam us-1800 through the headphone out. how can i do this? right now the metronome only plays through my computer speakers.
Yes, the Tascam is almost certainly not the problem. From the signal block diagram (p.23) the headphone amps receive a summed feed of all thru channels, or the usb return, or any mix of both.
This means that your monitoring is down to routing in Cubase, not the us-1800.