The best line conditioning would be dedicated one box per component. Not only do you minimize sharing AC noise such as digital, you would also be able to take full advantage of dedicated circuits/lines.
You might consider the Foundation Research LC-1 and LC-2 passive and dedicated in-line conditioners which also include their own power cable. So if you already have power cables, you can sell those to offset the cost of the LCs. The passive implies that they do not draw any current and with my 600 wpc amp into 4ohm load, I've never felt my presentation was lacking authority or PR&T.
Marty DeWulf rated the LC-1 and LC-2 as the best he's heard in the Aug, 2003 issue of Bound for Sound. That was the old version. Six months ago, I purchased the new versions and I can say that as good as the old versions were, the new versions appear to be multiple times better.
The LCs do not include surge or spike protection, nor would I think you want such a feature as this is usually compromises the sonics (from what I hear).
A new LC-1 (for pre or source) runs about $700 and a new LC-2 is $900. If you can find used ones, I know that Foundation Research will upgrade the old versions for about $50 or $60 each.
-IMO
