Dynaudio Special 40

I had the c20s for a little while. IME unless the Special 40s are substantially easier to drive then that Arcam would do them no justice at all. 

Brother in law has these in 12’ x 20’ room w EL-34 powered VTL - really good sound, easy load - you should be fine IF you keep SPL reasonable 

I am currently driving my Special 40 with an EL34 tube amp that is 35 WPC and it has plenty of volume for me for moderate listening levels. I cannot rock the house like I can when driving my Klipsch Heresys, but I don't typically need to play that loud. The 40's already have terrific bass, but I found that by using a sub I can get substantially more volume because I can set the high pass filter on my amp to match the crossover of the sub thus freeing up the amp from much of the low frequency work. It is really a great sounding combo.
 

My room is 27’x13’  Assuming I purchase the Special 40. The speakers will be placed on short side of room. Listening distance would be 10 feet.

The S40 is a very easy speaker to drive..The impedance never drops below 6 ohms & it is Phase corrected so its an easy load on any amp..As you have moderate listening levels & if your room is medium/ish 85wpc.is plenty of power..That said the S40 is a high resolution monitor & not extremely forgiving of poor amplification so I hope you have future plans for an integrated amplifier more worthy of the S40,which I consider one of the top 3-4 stand mounted speakers available at any price & a stone cold bargain compared to other so called TOTL speakers..

Ill get you that answer monday or tuesday. 

how big is the room?  key factor in answering your q

FWIW, I've heard this is an especially difficult speaker to drive well. I know it's not all about wpc, but I have a suspicion that 85wpc will make it loud enough but won't make them sing.