I know the 680 is the more sought after model but, is there really a big differance in sound?

They do look very similar but the 680 maybe slightly cleaner lines.

I do want one but not sure which, do either have line in?

Thanks

get the 990 or the 680 yes they do have a line in ,  to me the 990/680 sound the same .  they do sound great .

990 has line in...680 doesn't but you can always use an FM transmitter

sorry the 680 has a line out my bad

http://www.ebay.co.uk/itm/panasonic-rx-dt680-stereo-/200789492605?pt=UK_AudioTVElectronics_HomeAudioHiFi_CDPlayerSeparates&hash=item2ebffc837d

"needs new radio reciever part", seems a bit of a deal killer, it looks great.

680 is the street sleeper   you need one in yer collection

The 610 doesn't have line-in either (I have one).

The 610 sounds good, for sure, however the 680 has bi-amped & bi wired mid/tweeters & woofers, compared to the 610's single full-range drivers (with pointless piezo tweeters). I suspect this will make a considerable difference, sonically.