New Dynaudio Heritage Special..?..!

Not sure I'd recommend either upgrade path - if you love the S40s, why upgrade?  The HS is IMHO a better speaker, but a different sounding one.  Still a Dynaudio, but a more refined/laid-back vibe.  

I haven't heard the Benchmark, but it is a powerful amp. Thinks would probably improve by doing monos in a pair, but again, not sure what you are trying to improve?  If you love the sound of the S40s and the amp, I'd look at spending money on sources, power, acoustics before adding an amp or changing the speakers.

I'm the OP...😉

just took delivery of a pair of Heritage Specials.

nice surprise.

Great news. I am a fan of mid sized monitors too. The Heritage Special should offer an improved and grown up sound from the S40 that you currently own. 

Enjoy ~

Joseph Audio Pulsar Graphene is 9K and Silverline SR17 Supreme is 7.5K,.

It's not as if the Heritage Special is in a price category of its own. 

I wasn't aware that affordability was a hallmark of this hobby!

@ianrmack - Congrats!  Do share your observations when they have settled in.