I'm afraid I can't be of much help. I use the receiver in 5.1 mode with Piega speakers. I haven't noticed the reverb in any sound mode, not even with AllCh Stereo. I assume that you have done the calibration with the microphone (?). But even if you didn't, there shouldn't be any reverb. And are the distances displayed after the calibration approximately correct? For my part, I am quite satisfied with the sound, except in DAB+ mode. There I perceive an unnatural distortion that I didn't have before with the TX-NR818. This one also had a finer resolution and was better in terms of sound. But unfortunately without DAB+. Classic stereo operation without a subwoofer is also difficult to achieve with the TX-NR6100. In quiet mode, the subwoofer suddenly switches off, which is also a bit annoying. I would like to replace it with the TX-NR7100, but it seems to be out of stock for months. Unfortunately, the even larger models no longer fit in the lowboard because they are too high.