You aren't going to find anything that could go inline between the DVD player and receiver, because such a device would have to both decode and re-encode DD and DTS in order to preserve those 5.1 tracks. It really does need to happen at the receiver. My channel trim idea could be a permanent adjustment (basically leaving the center 4 or 5 dB "hot" relative to the rest of the system), which would reduce the effectiveness of the surround system, but it really isn't as optimal a solution as a receiver-provided feature like a night mode. What's the model number of that receiver? Might be curious to see if there is something hiding in the Sony's menu that could provide a capability similar to night mode. Another option would be to find a few examples of the objectionable swing and figure out the exact nature of the loud passages - it could be something that adjustment to the sub trim could help with (if it's excessive low freqs that are getting to him), for example.