The visual differences in the TV upgrade will be more noticeable than any audible differences, if any, when upgrading from the Marantz 6012 to something else. If the eARC update to the Marantz 6012 works properly, a device supporting 4K @120Hz can be directly connected to the LG C3 with no loss of audio quality when playing uncompressed multichannel signals from directly connected devices. What is it exactly that you feel is lacking in the 6012?