I understand that Dynaudios are power hungry speakers and really start to sing with high power so I'm wondering if my Arcam is enough to drive the Dynaudio Contours.
That is such a die hard myth. Yes it can true for a speaker such as this, but is not true in all cases so your Arcam may be very adequate, or not but a speaker that can handle 300 W per IEC does not need 300 W or even 50 W to "sing". For argument sake, in a 12X 15 room sitting 8 feet from a pair, they will sing very well for you even with a 50 W amplifier, if you play some studio recordings of Jazz music like Diana Krall, Patricia Barber's.
Take a look of the relevant factors such as your seating distance, desire sound pressure level and the speakers sensitivity and impedance and you'll have the answer.
Specs of the Contour 30:
IEC power handling: 300W
Impedance 4Ω
Sensitivity: 87dB (2.83V/1m)
Now you can us an online calculator to get a rough idea, such as the following:
Crown Audio - Professional Power Amplifiers
Peak SPL Calculator (homestead.com)
And take a look of the following examples based on the speaker specs and the calculated results based on 1 speaker and seating distance 3 meters and assume no room gain:
Example A, you want reference level (105 dB max peak), you will need 1133 Watts.
Example B, you are okay with 10 dB below reference level, you will need 113 Watts.
Now if you sits closer, say 2.5 meters, that's about 8 ft:
Example A, you will need only 787 W
Example B, you will need only 78.7 W
So you can see it depends a lot on the distance and your desired SPL.
Also consider some facts:
1) 10 dB below reference is still loud enough for a lot of people, in fact a little too much for me.
2) The calculations above are based on THX standard, in practice, for music, most of the time two speakers will be making sound at the same time, so it is reasonable to expect 2X the SPL, and the power required for the same SPL will be reduced by half.
3) It may be reasonable to expect about 3 dB of "room gain", but room gain mainly affect the bass so that may be the reason why the Crown audio calculator ignore that factor.
4) The power handling rating of the speakers ultimately limit the maximum requirement if you want them to have a long live.
To gain 3 dB SPL, power requirement doubles, conversely for 3 dB less, power requirements will be halved.
The Contour 300's power handling spec is 300 W (IEC) so if you want to leave no doubts and not bother with any calculations for different scenarios, then you should get a power amp rated minimum 300 W into 4 Ohms, or 500 to 600 W into 4 Ohms if you want to have ample head room.