Upgrade to sound quality of Dynaudio Heritage speakers

I would echo @bluethinker ’s thoughts particularly with the Gryphon Diablo. I don’t have experience with the Pass Labs INT25 but suspect it’s around the Luxman’s capabilities in driving power. I recently upgraded from the Luxman L-590AXII to the Gryphon Diablo 300 and it’s truly and ear-opening experience for me, and I’m extremely pleased with the result. My Marten Duke 2 speakers aren’t really inefficient as it is high sensitivity when compared to Dynaudio Heritage Special, and I suspect the Dynaudios are even more difficult to drive than the Marten. Get a good reference amp capable of driving the Heritage Special to its full potential and I’m sure you won’t be disappointed.

Let me relate my experience to you and I’ll make it short since I presume your experience or dissatisfaction with your current system, or Pass Labs INT25 mirrors mine as well. At times when music doesn’t sound good to you, lacking detail, dynamics and bass, and you want to hear more of the bass and dynamics. So you turn up the volume in an attempt to hear the dynamics. Sadly, music still doesn’t sound engaging as it still lacks dynamics, and the bass still sounds weak or not satisfying enough. The only difference is music sounds louder but the dynamics are still not present as the overall sound presentation is soft, mushy or unengaging. That will all change when you acquire a competent amp to drive the speakers to their full potential. Although you listen at low to moderate volume levels, everything will sound perfectly balanced. The dynamics, detail, bass and everything it’s all there. It’s a complete and satisfying experience if the speakers are driven to their full potential.

The Gryphon Diablo 300 entirely changed my perception on what a good amp is capable of. I’m sure there are other alternatives out there so pick one which suits your budget and preferences. I’ve tried the Gryphon and to me, it fits my system very well. Before I bought the Gryphon (which comes with the built-in DAC module), the Vitus SIA-025mk2 and SIA-030 were also considered but these amps although used particularly the latter are considerably costlier than the Gryphon Diablo.

Good luck.

@jmascian and @woots +1 on the Burmester 032.   I use it paired with Vivid Giya G 3 speakers.  Sophisticated, clear, and true timbre.  Solid state speed, clarity and dynamics with tube like staging, imaging, and treble reproduction.   Used is in the budget.  
If you go for speakers and can get past their aesthetic, there is no better IMHO than the Vivid Giya G3.  Read pro reviews.  All accurately describe their fast, dynamic, dimensional and accurate sound with a liquid and clear treble and midrange, and deep, powerful, detailed and tuneful bass.  

Pass Labs X series amps?

The Benchmark AHB2 would manhandle the dyns. Only question is would you like the combination. Much less expensive ($3500) than a lot of other amps. Hell, you could get two and run them as monos.

E.g.

I’ve had the AHB2 for the past few weeks, and absolutely love it! Paired it with Hyperion HPS-738s and Dynaudio EX34s. Dead quiet, wonderful bass control.

I’ve installed some Neutrik NL2FX connectors on my speaker cables and not sure how much of a difference it makes in comparison to the regular binding posts, but I sure love having the option. It’s a solid connection for sure.

So much impact & clarity for such a small amp. Thinking about picking up another one in the near future to run as monos.
https://forum.audiogon.com/posts/1846179

@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. 

@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. 
 

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! 

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. 

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

you have very nice gear, but i do note that your dynaudios are quite inefficient at 85db and your amp is rated at only 25w/ch, though pass puts out more real-world power. i'd be looking a more powerful, >100w amp--others will weigh in on the best in your price range