" ...I was disturbed that the DALIs don't really handle low bass as well as the Vienna Acoustics, losing the harmonic richness in a Johnny one-bass-note kind of response below a certain frequency. Given the price and size I'd expect much better bass resolution."
Are you sure that it is the speakers fault? Given their price and size and REPUTATION, I would suggest to investigate if they were properly controlled to begin with.
I read on Spectron web site that rms power is very misleading number because in "rms" sort of mode you really need 1-5 per cent of this power ONLY. However, when push come to you know what.... amplifier must handle it and it may be hundreds times greater them "rms"..
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Spectron claim that their amp is stable up to 0.1 Ohm and during the "stress" can deliver 3500 watts over 500 msec.
Next, and it may (or may not be important) that peak voltage even for medium efficiency speakers is more then 100 volts and all solid state and class D amplifiers that I know (except Spectron and Mackintosh) have rail voltage of about 65 volts - thus if signal is 100 volts then its clipped.
It could be that you have incredible speakers which are very sensitive to the signal they are asked to reproduced... and they are simply doing that whereas other speakers mask it
All The Best
Rafael