Denon AVP-8000 DTS upgradeable?

Does anyone know where I can send my Denon AVP-8000 DTS for upgrades (e.g. multi-channel decoder inputs and more current audio features)? Denon USA advises there is no further upgrades to my AVP-8000 DTS.
You can use the multi-channel inputs and let your DVD player determine the sound.
Unfortunately, the Denon AVP-8000 does not have multi channel inputs.