Don't know about the NAD but the Naim XS w/HiCap really made my C1's sing. Great match up. Supernait is also great.
That being said I came extremely close to getting the supernait but then I heard the Octave V70SE tube integrated and that's what I bought. Not sure what your budget is.
Wyred4Sound STI-500. $1995, Can't do much better at that price, IMHO.
Yes, they like lots of SS juice.
Icepower works well with these Dyns.
The Wyred integrated is where I would probably look as well.
Right now I'm using a VTL IT-85 integrated with my Dyn Special 25's. It sounds surprisingly good and drives them well. I have tried various solid state - Classe', Luxman, but really prefer tubes...
With those speakers I would not go with tube gear. They already have a beutiful smooth sound. Special 25's are very different. For contours I would go with solid state. You will definately get significantly better sound with a better amp. The NAD is a good budget amp, but you are missing out on what those speaker can do, for sure. I would consider a Plinius 9100 or 9200 if you can swing it. Also consider Bryston B100. Another good choice would be NAD M2 or M3. If you have a tight budget look at the NAD C375bee. No better amp for that money and it will make your Dyns sing.
I have the NAD M3 and right before this I owned a Wyred4Sound STI-500. My speakers are power loving Usher BE-718 monitors similar to your speakers. The NAD is (for me) much more satisfying for my taste and system synergy. It also has the outstanding feature of a variable high pass filter on one set of pre-outs so I can integrate my pair of subwoofers with the Ushers. If you currently do or plan to use a sub in the future this feature is pretty unique and absolutely effective.
Now I can fully crank electronica like Underworld or Crystal Method and the Usher woofers don't look like they're going to fly out of their frames while the pair of JL subs get to have a field day and go crazy. Really refined too on folk, jazz , classical, and most everything.
The W4S more extroverted-wider and deeper soundstage, more upfront detail across the freq spectrum, and outstanding separation of instruments. Just phenomenal with the right recordings. Unfortunately with the Ushers it was beamy, metallic, and uncomfortable sometimes as well. The M3 is meatier overall, much more forgiving of bad recordings, never quite phenomenal but always really good and doesn't leave me wanting. The other nice thing about the M3 is that the louder you play it the better it sounds. It gets fuller and stronger without getting more forward.
I haven't heard your speakers but if they are laid back the W4S is a great recommendation. If they are a bit forward the M3 is a good alternative. They both have high-quality stepped attenuators which I have convinced myself is a great feature. That's my two cents' worth after I read the good recommendations above.
I would go with the voice of experience -- users with relevant Dynaudio experience, that is -- and there are plenty of Dynaudio fans/loyalists around in the various forums. In other words, don't jump too fast for some reputed "high value" amp proposition that "should" work: check out the candidate(s) with current Dynaudio users. You don't always get the opportunity to tap into the experience of audiophiles who are SOLID, long term users of a particular brand exhibiting some notable consistency in their design perspective and "house sound" over the years; so don't miss the chance to get fixed up with something really special in terms of synergy.
More up my own alley: In reference to Cmo's observation above, I'll just pass along FYI -- nothing from my own experience -- Haden Boardman's conclusion from his review some years back o the Special 25's (which seem to have been given a second life by Dynaudio) in U.K.'s "Hi-Fi World" magazine. He claimed that the Special 25's matched up very well indeed with his own-design TEN watt EL-84 PP Class A integrated! Let's assume he was talking about a modest English parlor room, and that Haden isn't into Techno-pop or Slayer. No, the on-paper spec would not suggest that this could be right; but more than a few approximately 86 dB sensitive speakers have somehow managed to pull off such minor miracles, under the right circumstances. Is the Special 25 an anomaly among compact Dynaudios? Dunno -- just something from the FWIW dept., in consideration of this suggestion: that a well-chosen small PP tube amp with good iron off eBay and PROPERLY refurbed/updated can be just about unassailable in the bang-for-buck rankings playing 80% of what an Audiogoner might care to listen to (n.b. the qualifications). As some proposed SS candidates for typical Dynaudio scenarios above might suggest, finding solid state with some grunt that really convinces overall may be a considerably more costly proposition. Perhaps this will be useful to someone.
Postscript to my comments on the Special 25 and tube amps (as I couldn't seem to edit, having "previewed"): The Class A part may be key to Haden's reported experience with the special 25's. Most of the vintage PP EL-84/7591 amps up there on eBay have a cathodyne, or split-load, phase splitter/driver circuit. This circuit should really NOT be used with anything but Class A biasing of the output tubes for a very straightforward reason: balance between the two drive signals depends absolutely on the plate and the cathode sections of the driver tube seeing EQUAL IMPEDANCES -- this cannot be the case ACROSS THE FULL AVAILABLE BANDWIDTH when one or the other of the output tubes is cutting off! Also, it's possible, though not so probable, that Haden's amp had grid chokes on the output stage, or some other means to dump off any appreciable grid current which can lead to "blocking" in connection with the time constant of the coupling caps in circuit. Pushing a little amp hard is, of course, more likely to make such conditions unpleasantly obvious in the listening.
A used mf nu-vista m3 or a5 if you are on a budget
I had the Bryston B100SST and to me the Naim XS and Octave V70SE just destroy the Bryston in every way. I traded in my Bryston for the Octave. Both the Naim and the Octave are high current integrateds and the Bryston is not. That being said I fought my audio dealer for over a year thinking the Bryston would be too hard to beat. Well an in home demo proved me wrong in the first 10 seconds of listening.
The 1.3 mkIIs can be a touch hot sounding on the top end with some amps and are a tad towards the warm side of sound overall.
That and their appetite for juice makes Class D amps a very good option.
Toe out/indirect tweeter orientation can be used in placing the Dyns to help tame the top end as well if needed. Thtend to image and sound best this way in general I have found
I owned these speakers for some time before moving up in the Dyn product line, and depending on your room size and preferred listening volume, your NAD should be fine. Jaxwired is correct in that these speakers do not have the brighter treble some Dyn models are known for, so if you decide to change I'd look for an integrated from NAD, Plinius, Simaudio or other good SS manufacturers with more power/current.
If you want something different, by all means try a tube unit. Tubes can definitely provide a different sound, just as the same album may sound very different when played on a turntable vs via CD or DAC.