proac response d2 vs older 2

((((I found the D2 to be a bit strident at times.))))
I own both pairs.
I feel its actually the opposite compared to your experience.
My take is the older Response 2 d while a legendary performer almost always needed tubes to perform at their best.
Ask yourself, what were you using at the time, same gear, wires jumpers,
High Mass stands, Proper Toe In, set up, etc??
Either speaker will need 3 to 4 days of run in to fairly compare.
If both on a level playing field using Proac Sig black copper speaker wire,
even-handed neutral electronics, you will find both are very similar speakers while the newer response D2 a bit more versatile less bright, will play slightly deeper work with decent solid state or tube gear while staying together or more effortless performing complex music.
Best, JohnnyR
Proac dealer

Comparing the D2 to the 2S.  I like the 2S much better.  They both image like ProAc is famous for. I found the D2 to be a bit strident at times. 

I've compared the two, side by side in the same system. I felt the older 2 was warmer.