dont really understand this

but.....
got a BT vision box other day, connected with just HDMI lead, sound and picture very good.
new DVD arrived today, Samsung 1080P7, wanted a cheapish HDMI upscaler with optical out so seemed like good option.
connected to TV with HDMI, optical to amp, picture very good, sound from TV speakers but not getting 5.1 from from my surround system. Audio options in DVD have PCM or Bitstream, switch to Bitstream, now get 5.1 but no sound from TV speakers, and a (brief) message on TV saying "HDMI audio not supported"
manual says when using HDMI also connect audio leads (red/white) from DVD to TV, did that, still no sound from TV speakers, only way to get sound from TV is to switch back to PCM.
Can't always use my surrounsd system as Kids room is above but can't find any settings in the player menu that will give 5.1 through optical out
and sound through the TV speakers, which seems odd as I assumed the red/white audio cables would solve that
Dont really want to have keep going into the player menu to switch between the two, any ideas?