Diablo is 100% like grand EM in higher midrange and hights, the only diference to my ear is dynamic, because it has atenuated tweeter by 9db. Actualy I have ablity in home on my equipmnet to compare Diablo,Scala, Maestro(which is unreleased to public yet ) and yep.. - grand EM(Grand EM without 16' inch Em woofer just top 11 inch woofer ) side by side. If i would be customer i would buy Diablo(because it cheap for what it offers) or Nova EM, nothing worong with scala ,its very good sounding just no major diference in bass comparing with Alto , if talking about Maestro its just for bigger or bass hungry rooms, but its not Scala with aded woofer - sounds diferent from Scala in midrange, its more like grand EM, but still nothing revoliutonary change in bass from Scala just more extended and punchy . Nova is EM is another major improovement and step . however in that price range there lot of other fine speakers. Grand EM is for big boys with big rooms.. as for my opinion if there were released not Scala but Scala with EM it would be very sucesfull speaker and offer one of the best sound and technology for the money. I still think diablo is very good value for the money I tested Sonus faber audiotor M and even big cremona M against the diablo and it was clearly that diablo is better speaker it has the same musicality as sonus faber even more, but it does it on high end way-not coloured . One negative thing for the diablo is that it no very sensitive(arround 84-85db/w/m which is not bad as for monitor) and needs at least 30wats an shines with 100w amps
As for raidho and Tidal I can not say anything as I do not familiar sonicaly with theese brand (at least Tidal) so you need to hear them by yourself and compare.