You've got TWO Arcam P38 105w/ch to 8 ohms amps. I can't imagine that they would not do a find job of driving the Helicon 800's, especially since they are Arcam amps.
Now, more power is always a good thing, and the Helicon can handle amps up to 400w according to the specs -
Recommended amplifier power [W]: 50 - 400
But also consider this -
Sensitivity (2,83 V/1 m) [dB]: 89.5
Maximum SPL [dB]: 113
Those are reasonably efficient speakers.
I think the amps you have will do a fine job, but it gets down to the size of your wallet.
I assume since you have two amps, you are bi-amping. The 100w amps should be far more than enough for the mids and highs. So, if you insist on upgrading, I think you would only need to upgrade one of the amps. The amp that is on the low frequency section.
Keep in mind that in the standard orchestral power distribution, the power in the low range, below 500hz, is 5 to 10 times what it is at higher frequencies. So, the mids and highs require far less power than the bass range.
Though, what amp would be a good upgrade, I'm not sure.
Personally, I say try it with what you have and see how it works. Then if you feel you need more, upgrade the low frequency amps (assuming you are bi-amping), and give that a test. If you are still not satisfied, them perhaps consider upgrading the high frequency amps (again, assuming you are bi-amping).
Start from where you are at, and keep going until you get to where you need to be.
Steve/bluewizard