An affordable AV receiver is always a good option to consider, so Onkyo TX-NR555 vs Denon AVR-X4000 comparison definitely makes sense. Both have 7.2 channel amplifiers. Only the TX-NR555 has a Dolby Atmos support. DTS:X is supported only by the TX-NR555. We have evaluated both AV receivers, TX-NR555 has an overall score of 7 out of 10 vs 7.6 out of 10 for AVR-X4000.
The Denon AVR-X4000 is better receiver in this comparison. Check Denon AVR-X4000 price