pardon me for unable to advice further on HTPC as I'm not a user on that field... my initial reply was made base on your mentioning of 2 premium players and the plasma TV.
get a budget friendly Bluray player, set it to output video signal to 720p. that's more than enough to let any new TVs to do a second layer upscale to 1.4k image.
a straight double jump from player upscale to 1080p, follow by TV’s second layer upscale to fill up the screen automatically, worsen...