can i still use a sub with only hi level inputsYes, assuming it is a powered sub (that has its own internal amplifier), and that it provides separate high level inputs for the two channels. Connect both the main speakers and the sub's inputs to the integrated amp's output terminals. You can use very narrow gauge wire for the connections between the amp and the sub, because the inputs of the sub's internal amplifier will draw negligible amounts of current.
Regards,
-- Al