As someone who has helped friends upgrade 2 pair of speakers (RP-600M and KLH Model 5), I can tell you, Danny’s upgrades improved every aspect of each.
With the Klipsch, his upgrades made an unlistenable (to me) speaker, into something that was pretty reasonable. With the KLH, the improvements were less obvious, but still worth the effort.
The things that Danny improves are not just a matter of ’re-voicing’ the speaker, as some have accused him of doing. He is correcting demonstrable bad engineering. As if a competent speaker designer would make a choice to have bad phase relationships at the crossover point, or tons of stored energy, etc.
Of course, designers designing speakers to meet a price point don’t have much of a choice to use inferior caps, iron core inductors, sand cast resistors. But how is that Danny’s problem, and not a detriment to the quality of the end results? Cheap crossover components are sill cheap crossover components, and inferior sounding,
As far as Danny not being a trained engineer, therefore casting doubt on his credibility, that also doesn’t mean a whole lot, IMO.
I spent years in my youth, helping a friend upgrade speakers, build speakers, upgrade the acoustics in restaurants and other public spaces, rebuild enclosures, and other related things.
He had no formal acoustics or engineering training, yet he went on to work for Harman Audio on the design team responsible for Revel speakers.
Let me add, that I am not associated with GR Research, nor have I ever owned any of Danny's products.