Upgrade to sound quality of Dynaudio Heritage speakers

What specific improvements are you looking for?  Here are three integrateds just fyi I’d have to think would be a significant upgrade and certainly worth a look.

https://www.usaudiomart.com/details/650194713-vitus-audio-sia-025-mk-ii/

https://www.usaudiomart.com/details/650176303-gryphon-diablo-300-with-dac-and-phono-stage/

https://www.audiogon.com/listings/lisbcb3g-vitus-audio-ri-101-solid-state

Good ideas @soix. OP, there is also an 032 listing for a beautiful Burmester integrated for sale on Audiogon for $12ish. I have an older version of this and the sound and power are amazing. I also have Burmester amp and pre-amp in my main listening area.   The dealer who has this listed also has Vitus and Gryphon previously owned available as well. Good luck and let us know how you make out. 

The Boulder 866 is a fantastic integrated. 200 w @ 8ohm and doubles to 400 at 4ohm. It would have complete control of your speakers. Good luck! 

@jmascian - As noted by @loomisjohnson - The Dynaudio Heritage Speakers are not efficient speakers. I also own a pair of Dynaudio Heritage speakers and know, from experience, they need a more powerful amp to open up. 

I initially used a Luxman 590axii which was recommended by the dealer. That turned out to be awful advice. The Luxman 590axii is a class A biased amp that is advertised as 30 watts in class A (8 ohms). Apparently, the Luxman has been measured to go to up to 90 watts in AB (8 ohms). That said, the Dynaudio Heritage Speakers sounded anemic, and overly focused on the treble, when I drove them with the Luxman. Bass was largely missing. 

Let me cut to the chase: You need a dramatically more powerful amp to open up those speakers! 

I ultimately purchased a used Gryphon Diablo 120 which is 120 watts in 8 ohms and 240 watts at 4 ohms. It's a high current amp. When I hooked up the Dynaudio Heritage speakers it was an entirely new experience. The Gryphon opened up the Dynaudios and the speakers immediately started singing with an utterly balanced delivery. Bass came alive. Treble was clear and balanced. The synergy is fantastic and will make you appreciate your Heritage speakers. I was thinking of selling them before I paired them with the Gryphon. 

You should be able to pick up a used Gryphon 120 for under $7.5 (without internal dac) or at around $8K with the Gryphon dac. My version came without the Gryphon dac. 
 

@jmascian @soix - As Soix mentioned, the Gryphon 300 would be an excellent pairing with the Dynaudios. That amp would bring the Heritage speakers to life. Big Time.