Henk, what SS amps have you found really work, esp biamping Divas?
My preference if SETs are impractical is at least to go for a SS amp that is a close analogue in sound character ie tone rich/dense, creamy, veering towards dark, or more a Gryphon type character than Krell
The damping factor is simply the ratio between the resistance of the driver and the resistance of the rest of the circuit.
In practice, the resistance of an apogee driver, it being a bass, a midrange or a tweeter is somewhere between 0.1 ohm (the scintilla midrange) to about 3 ohms (diva bass, duetta bass etc)
The resistance of the rest of the circuit is made up of the sum of the amplifier resistance (usually < 0.05 ohm for an ss amp) and the filter resistance, because both of these are in series with the driver.
So the lower the resistance of the filter, the higher the damping factor will be. Simply because the speaker filter has a higher resistance than the amplifier. So the published damping factor of the amplifier is usually quite meaningless.....
It gets even worse: At the cross-over frequency between two drivers, for instance the bass and midrange, the filter resistance is equal to the resistance of the separate drivers, so here your damping factor is equal to 1.0
This alone is a good reason to go active bi-amping
Nevertheless as you may have seen I have an amp with switchable damping factor and you can just about hear a difference between its low and high settings.
The A21 assertion that the bass sounds somewhat over-controlled or choked due to high DF is just a guess that may well not be true. It is kind of based on the switchable DF amp and the effect thereof i.e. subjective stuff.
I did state earlier that the effect of amp DF on Apogees is very marginal indeed.
I'm basically saying keep a constant flow of amps running past your speakers until you find ones you like. There's no other way.
Another review claims use low resistance speaker cables or you can lose up to 15% of your amp's power. Not seen that one before but might be worthy of some consideration if using tube amps.