The first A5 is driving a pair of "Cyburgs Needles". The Needle is a pretty famous mini TQWT that suits a wide range of 4" full range drivers. In this case I'm useing the Dayton Audio RS100-4 and they're great.
Here's one example of the construction plans:
www.acoustic-design-magazin.de
View attachment 419364
I did not built these myself but got them 2nd hand for 20 bucks. For the pair! The ugly non-fitting screws have been replaced in the meantime.
There are two more reasons why they sound so good:
1) The bass is offloaded to a cheap Monoprice "Premium Select 8in 200-Watt" Subwoofer. So the TQWT is mainly a convenient integrated stand

. I got it even cheaper than cheap for 99 bucks during an Amazon sale.
2) A WiiM Ultra (the most expensive piece of kit in this chain) is handling subwoofer integration and RC equalization (manually developed using REW in this case). If WiiM would finally hear my plea and implement separate speaker EQ and room EQ (like Lyngdorf do) I could even get rid of the passive notch filter.
This combo has previously bee powered by a pair of V3 Monos. Without making any further claims I will just report that I enjoy more listening time since the A5 arrived.
In this use case there is really not much demand for sheer power, but the legendary "clean first watt" is what matters most. Spending most of the budget on the front-end and the least on speakers goes against conventional ASR wisdom (which by coincidence matches neatly with dealers' sales margin being the highest with loudspeakers). Nevertheless I'm absolutely sure it was the right thing to do.