About the power missmatch:
1)Having poweramp less powerfull than driven cabinet is not a danger and not a problem in any way.
You are just not pushing them cabinets to their maximum possible power.
That happens every time you are not running your car stereo, radio, TV or any other audio device at maximum volume.
2)Trying to use more powerfull poweramp than the cabinets will most likely end up burning out winding wire in the speaker coil.
In the very same fasion like filament wire burns out in an old lighting bulb.
About the resistance missmatch:
1)Having poweramp output resistance greater than the driven cabinet resistance (for instance: poweramp 8 Ohm, cabinet 4 Ohm) will damage your amp.
2)Having poweramp output resistance lesser than the driven cabinet resistance (for instance: poweramp 4 Ohm, cabinet 8 Ohm) will reduce your poweramp power (twice for my given example numbers), reduce sound level and will distort your sound in a particular way.
If I'm correct this is simmilar to operation of guitar power attenuators.
That bass amp probably will not sound very sweet as it is a solid state.
Ones who use bass amps with guitars mostly use ALL tube amps made by sunn o))) or Ampeg.
As for HI and LO input, bass pickups (and signal) are generally weaker than guitar pickups (and signal).
Most of bass pickups have output similar to very mild, very vintage guitar single coil.
You just need to try both and decide.
