Hi
Denon and Marantz are both made by the same company i.e D & M holdings.....Marantz is indeed more warm and musical....but never lacks performance in HT ,,,,,, Denon is more tuned towards HT performance but lacks punch in music....
There are dedicated Owner threads of Denon and Marantz on this forum where you can read upfront user experiences.....better still is to audition each of these AVRs and decide for yourself. Marantz offers auto calibration for all their models while Denon offers it for their mid segment to high models....
Your source material, the interconnect cables from sources to TV to AVR and to speakers also need to be of decent quality to get optimal performance.
A neutral AVR would be Pioneer or Yamaha......you could also check those models.....
All the best!