How to connect external speakers to plasma TV

I want to connect external amplifier & speakers to my TV which has a digital optical audio output.Can I connect the TV digital optical audio output to the digital optical
input of a D/V processor converter (with the analog coaxial
output connected directly to an amplifier for the external speakers?)/or does the analog coaxial output of the D/V processor have to be connected to a preamp/amplifier setup?
It depends on the output of your TV and/or your specific DA processor. Some TV's offer the option of line level or speaker level outputs and some DA processors include a volume control.
What you are proposing should work fine, although I am not sure what you mean by a D/V processor... if you are referring to an Audio/Video processor that decodes Dolby Digital and PCM datastreams and has analog audio outputs and a volume control, then yes.
If you have Direct TV just take the analog output from the satellite box to the preamp. My Panasonic plasma also has analog RCA out which I have also used.