How much difference between Dynaudio C1 & Contour 1.3SE?

The S25 Fatigued' what amp were you running . My S25,s our being powered by the Accuphase A65 and they are far from sounding fatigued.
Of course their our many other factors that create that fatigued sound, source, cables, ac power, room acoustics or lack of. you don't see as many S 25s for sale as you do the C1,s for example in fact the last time I saw a pair of S25s for sale on AG was at least 4 months ago.

yes I'm a S25 fan.

At my dealer and he was running Sim Audio separates - Octave and Burmester with Nordost Valhalla cables. I thought the same with the Sapphires and Consequence UE.  For me the mids and highs were just too forward compared to the C1's and Contours. S25's like Sapphires were limited production. The S25's even had a second run. The thing about Dyns is they had both forward and laid back sound sounding speakers yet they all retain the 'Dyn House' sound. Everyone has their own tastes and expectations when it comes to what they prefer. I've read where some folks thought even the Sapphires were too laid back. Had a friend who had C2's and he thought they were too laid back and traded them for Sapphires.  About a year and a half later he traded those for C4 Signatures.

Audio appreciation spend lots of money............

I would not run the Nordost Valhalla speaker cables on S25,s , they have a reputation for being thin and fatigue sounding over time. The S25 s need a more organic cable like Purist, WireWorld, Crystal Cable, Crystal Clear. Sim Audio while certainly good I would stick with high powered SS Class A amps or high powered tubes.

The S25,s our special but they need a little more attention to equipment and speaker placement to shine , yes they our punchy and lively but with the right stuff they can sound quite nice.