Spiral bit works the best in my opinion... Doesnt really matter if its up cut or down cut for speaker holes, it just pushes the the dust created in that direction, up or down. I have the Diablo brand from HD or Lowes, cant remember, but its been good to me. Looks like you have a 3/4" or 1/2" round over bit in there now, Id pick up which ever one thats not. Those are the ones I use 99% of the time, Spiral Cut, 1/2" and 3/4" round overs. Only other I would look at would be a 1" flush trim bit, its has the ball bearing on the end that you can use to trim two pieces exactly the same.
Gonna guess that that router takes 1/4" shank bits. only the really big ones take 1/2" shank.
That router doesnt have a plunge base, but for speaker holes you can manually plunge the bit or drill a starting hole to place the bit in.
