jeroen_d

This is always very difficult to describe. I will mention the most obvious differences.

The millennium has a very metallic sound with cymbals. In the positive sense, that is, very realistic. It sounds also very open due to this capability. The top end however is a little bit recessed.

The scan speak sounds less open than the millennium, just like the HDS tweeter. But the overall tonal balance of both the SS and HDS is more on the spot. I think this is the reason they won't give you that special open millennium sound.

It is very difficult right now to describe the differences between SS and HDS, not having heard both tweeters next to each other in speakers with similar overall tonal balance. If you need that extra little bit of refinement, maybe it would be worthwhile to pay a lot more money and buy the SS7000 or 6600. These scanspeaks have a very extended response and have a bit better performance when multitone distortion tests are performed. When you use them from 2kHz and above they are unbeatable in this respect. See http://206.13.113.199/ncdiyaudio/mar...eerlessHDS.htm.
What you see in these tests, is that the performance of the HDS is very close to the seas TBFC/G. But what I have heard up to now, I like the sound of the HDS more. Don't know how come, maybe the very well controlled dispersion at the top end. I am under the impression that the HDS is very similar measurementwise and soundwise to the ss9700. It is a matter of personal taste which one you would prefer.