While I have no particular familiarity with any of those components, I suspect that both of the amplifiers you mentioned, like many in their price class, will not perform at their best when driving speakers having impedances that are low, or that are difficult in terms of phase angle. A good indication of that is the fact that the power ratings of both amplifiers into 4 ohms are much less than twice their ratings into 8 ohms.

As indicated in John Atkinson's measurements in Stereophile of the LS50:

In contrast, here are JA's corresponding comments for the Dynaudio speaker:

Hope that helps. Regards,

-- Al

As indicated in John Atkinson's measurements in Stereophile of the LS50:

The LS50's impedance (fig.1, solid trace) drops to 4 ohms at 200Hz and to 5.4 ohms at the top of the audioband. The electrical phase angle is generally mild, but the combination of 5.3 ohms and 41° at 135Hz, a frequency where music often has high energy, will make the speaker work at its best with a good, 4 ohmrated amplifier.I note also that the manufacturer specifies a minimum impedance for the LS50 of only 3.2 ohms.

In contrast, here are JA's corresponding comments for the Dynaudio speaker:

While Dynaudio specifies the X12 as having a nominal 4 ohm impedance, its plot of impedance magnitude and phase (fig.1) reveals that it doesn't drop below 6 ohms, and then only in the lower midrange, when it reaches a minimum value of 4.8 ohmswhich, like the combination of 6.6 ohms and 30° capacitive phase angle at 125Hz, will not tax any well-designed amplifier.So I suspect that the Dynaudio speaker would be a more optimal match for the Creek or Rega amplifiers (and most other amplifiers in their price class) than the KEF would be.

Hope that helps. Regards,

-- Al