Hello friend.
You're posting screenshots of IPR, which is fine. But I'm not really getting what you're saying.
There are a few things that I spotted in your render settings which I would change right off the bat without knowing anything about your scene.
Drop your GI clamp to like 10. The 1 million value never made sense to me but it clamps some of the brightest bits you may be generating with your image.
Coherent ratio, I like to keep at around 0.25 - 0.3 (Got from somewhere that it basically takes about 250-400 samples to clean up the incoherent colors but after that your scene cleans up faster)
There's also an issue with how you establish the power of your lights. All lights start off at 100 power, which is actually quite a lot. You should be getting along with 10, maybe 15 if you want to push something out of bounds. Under 10 is what I usually go for and I get decent results. Also, build everything to scale. Just makes things work in a more logical way.
But I don't really understand what you mean by grime. If you're using cinema 4d shaders, you may want to up the resolution you're getting under settings from 512x512 to 2k IF you're getting issues with that - if not 512 is fine. And your sky seems blurry. More so than out of focus would cause, so that is probably quite a low resolution image. Consider upgrading.
As for the medium emitter not working, which your only mentioning in the title, have you tried upping/turning on the transmission of your shader.
Also, you have to understand that a medium emitter is probably not the best choice for non volumetric objects because the emission is not controlled by any sort of density of the object. You get a solid form giving out light. So, if you emulate some sort of candle flame in TFD, or houdini and port it over into c4d, you're going to get a more realistic flame but also a more realistic light emission from that flame.
You may want to look at just using a blackbody emission in the emission tab because you'll get the same result, with finer control and a faster output (i.e. cleans up faster).
http://imgur.com/a/LHiOj
As you can see, upping samples helps but I don't see anything you would call grimey.
I did not use any textures in my image. No HDR to light this, the only illumination is from the sphere I crushed into the shape of the flame.
I'm using blackbody emission: temperature 2622 and power 0.5 [Surface brightness off, normalization on, cast illumination on].
For a blackbody emission I also set the transmission to 0 and the diffuse is a pure white.
The flame is 0.821 cm x 1.204 cm x 0.464 cm.
/ramble
