It's been my experience trying out different things. If you think there are class D amps out there that will sound better than my Hafler DH120's, let me know!
Given that they are well-designed and operating withing their capabilities, Class D will not sound different from any other well-designed amplifiers that are operating within their capabilities. Class of output bias has nothing to do with it.
This does not in any way imply that all amplifiers sound the same
in all situations. Some speakers present a difficult load, and some amplifiers cannot handle that load sufficiently. The common reason is that some designs are made to a price point, but it is also true that some listeners prefer a non-neutral, or deliberately inaccurate sound. The two examples that come to mind are some tube designs and some single-ended solid-state designs. Some manufacturers are willing to pander to the desires for inaccuracies.
Your Haflers do not fall into that category.
The standard method for distinguishing audible differences in electronics is a double-blind test (DBT). The video
below gives you the protocols and reasons why they are necessary.
If you were to undergo a DBT, I would expect that any well-designed Class D amplifier of sufficient power would be absolutely indistinguishable compared to your Hafler.
Jim