... how important is Damping factor in determining what amp to buy

Actually no. It **might**. Any loudspeaker can be overdamped- IOW

Atmasphere is correct in this regard.

An example was the Linn Isobarics and the Sara which were voice to have great bass with Naim amps of the day, that had 20 damping factor. When a big Krell (>100 damping factor)was put on these speakers they had NO bass, too tight.

This was because Linn designed these speakers with a very over damped (low Q) bass, so they only sounded good in the bass with amps that had low damping factor. (just another marketing ploy by Linn, who were in semi partnership with Naim in those days.

Another similar case to (damping factor, but impedance matching) is poweramps that have very low 1kohm input impedance that could only be driven with preamps with very low (<10ohm) output impedances, usually of the same brand naturally.

Cheers George 

Another new feature is a user adjustable Damping Factor feedback control that allows the user to adjust the amplifier’s output impedance by varying the amount of negative feedback. Impedance can now be precisely set to suit the listener’s taste, and to improve control of the loudspeaker loads to deliver best performance. The 4 possible settings are:
1. LOW -- Lowest damping factor, good loudspeaker control, most natural sound.
2. MED -- Better loudspeaker control, with some impact on sound quality.
3. HI -- Best loudspeaker control, with a little more impact on sound quality, but on speakers that need the control the sonic improvement is clear.
4. MAX -- Maximum damping factor, but sonic impact is noticeable

What’s the significance of adjustable damping factor? Far greater than you might imagine. The clue lies in the fact that it is derived from the degree of feedback, the higher the feedback level, the greater the damping factor. In this day and age it is easy to assume that all feedback is bad and that the less you have the better, but it isn’t actually quite that simple. There’s a world of difference between local or nested feedback (used within a circuit) and global feedback (that encloses it entirely). While feedback-free preamps are all the rage, feedback is critical to a power amplifier’s damping factor, just as Q is critical to a speaker’s voicing. Between the two, these factors have a huge influence over amp and speaker matching, and as Q is generally a fixed value (unless you happen to be using the large Focal Grande Utopias, with their adjustable-Q EM drivers) then being able to adjust damping factor to achieve superior matching is a major benefit, significantly broadening the type and number of speakers with which the amplifier can achieve really good results.

VTL offer four settings for damping factor: Low, Medium, High and Max. With any given speaker you will find that one setting is dramatically more musical, dynamic, involving and better integrated than the others. In my room and in most cases, I settle on either the Low or Medium setting. Those who crave a drier, more heavily damped sound might opt for the high setting, especially if the speakers are a little loose in the bass or the room is exaggerating the bottom end. I can’t really see anybody needing the Max setting, but it serves a useful purpose in establishing the continuum along which you are operating. Once you’ve heard what Max does to the music, you’ll treat the setting of the amplifiers’ damping factor with the appropriate caution and seriousness. It not only has a huge impact on performance, it offers a huge advantage in terms of choice and your amplifier’s longevity, should you (or should that be, when you) change your speakers at some point in the future. If the amp/speaker interface is the single most critical junction in your system, the Series III Signatures pull the neat trick of offering genuine adaptability, a serious benefit that’s not to be overlooked.