I would like to know about connecting 2 additional Philips speaker(which comes with Philips dsp75u) to Panasonic xh175 5.1 home theatre. I am sorry I am not good in understanding the compatibility issue if any between the two brand of speakers in terms of ohm, amp or power consumption.
My room is big and that's why I want to add additional speakers. I planned to connect these speakers with centre sound port. I am bit worried too with fact that will it break my home theatre system or other equipments plugin with home theatre due to incompatibility.
Your Panasonic will not be happy running 2 additional center speakers. You could damage it. The center is primarily for dialogue so it would be better to substitute a higher quality center speaker for the one that came with the Panasonic. Can't tell if it has enough power to play a better speaker or if you can adjust the levels correctly but it is unlikely that you will damage it by trying it.