Those headphones are 64ohms, so you'd be able to drive them ok from C3. I'm just concerned about this post that says they really benefit from amping in the low end. C3's low end is already rather neutral, paring a headphone that requires some amping to sound right may not be the right choice.
What about the JVC HA-S500? Can you get those in your area, they're only $50 - $60 and have a 250 page appreciation thread here. From what I read they have slightly emphasised bass which will work well with the Colorfly's signature.
Even the JVC does not look like its easily available, at least online :( I'll check out landmark whenever possible. How about an amp paired with the HM5s? (Jaycar have clones for much less, right?)