Samsung & lg have both gone the way of no analog out now mate unfortunately .
HDMI or arc seems to be the norm now , I had to replace a perfectly good working Panasonic 5.1 receiver because my newer sharp aquos would not pass 5.1 via optical , only via HDMI arc.
The older lg plasma set I had had no such issue but the screen itself went faulty.
Hence I have an absolute spare of old av equipment which is worth nothing but I can't bear to part with :-/
Re sound bar - no you wouldnt need the CE cross with the soundbar , it has a DAC inbuilt capable of coping with Dolby.
Its a bit of a all in one solution in all honesty.
& you'd go straight optical TV out to optical in on sound bar.
Yes , you'd use the 3.5mm headphone out with a 3.5mm to twin rca cable into the amp
That way the sound bar remote can be used for volume.
Unplug the cable from the headphone , audio will switch back to the sound bar itself (maybe nice for later night viewing when you don't want the Polks blasting out).
Obviously that headphone out could also be used for actual headphones aswell .
You've got Bluetooth connectivity built in , a USB port for mp3 audio , & an extra 3.5mm line in for the echo dot if youd rather use it wired. (Also good for plugging in iPods or mobile mp3 players)
Like I say , an all in one solution , not perfect but the sound bar itself may actually offer good quality sound too , reviews actually look OK which is a bonus.
Vs a second hand avr ?? Up to you mate , if you were fkimg that route I'd puahbyou to look for something decent with HDMI arc over just optical though.