I have been using an STR preamp for nearly four years now and think it’s an excellent unit, especially if you want DRC and/or subwoofer integration. A friend, after hearing my system, went out and bought one.
One alternative is the miniDSP SHD. We have one in our TV system. I would prefer the Anthem on several counts, including better appearance, better customer support, and much much better display and user experience. I have been unable to compare the sound as the setups are completely different. ARC is IMO easier to use than Dirac.
The Legacy Wavelet has to be reprogrammed by the dealer if you change speakers, subs, or crossover settings. That ruled it out for me.
I have not tried the DSpeaker X4. An audiophile friend who did, had trouble. I can’t remember if it was an unethical dealer or trouble with the X4 itself.
The Trinnov Amethyst has not been updated in many years. It has a fan that some reviewers have found audible.
Hope that helps!