Renaat,
Okay, it sounds like your unit should be finished breaking-in, and since you're not running through a preamp, there's no mis-match or overload going on.
Power filtering is always a good idea. There is a lot of radio frequency interference and noise on your power lines, and its being injected into your system. That can cause a headache. Some equipment is more susceptible to it or more revealing of it, or both. When you try a filter that hissing HF noise will be gone, and you'll wonder why you ever listened witout filtering!
Having said all that, (and contrary to what you said in your last post) the Siltech website says that the Octopus 8-Way Mains Distributor does have filtering capabilities.
However, that doesn't stop RF from getting into your system through poorly shielded interconnect cables and speaker cables, which usually aren't shielded very well or at all. The longer your speaker cables are, the worse it can be. Make sure power cords aren't running next to your speaker cables.
Many silver cables are just plain harsh-sounding, lots of detail, but awful high frequency ringing, sort-of like metal tweeters. (You don't happen to have anything like those do you....? :-) Your new DAC may be more revealing of inadequacies downstream.
Jason made a good point - make sure you're speakers are hooked-up in phase. It may sound silly and very obvious, but I've walked in to many stores and CES exhibit rooms and found "professionals" with systems hooked-up out of phase! Dead giveaway: no centre image, particularly noticeable with a single vocalist at centre stage.
It's hard to diagnose over the Internet, but those are afew things to consider.
