Yes the built in Cineform codec is the same as the Aspect HD codec you can buy, just you cannot change from the standard setting. With Aspect HD you can set it at low, med or high as it comes in and the same when making m2t files from it.
Also with Aspect HD installed, Prem Pro will be much more responsive even though its the same codec and they give you a heap of realtime effects
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Encode out a small high res wmv clip and post it, so we can see the banding to make sure it's not you screen/graphics port. It will show up in the wmv file if it's there.
I also found Main Concept Pro's m2t encoder was better that Aspect HD- Prem Pro's.
Go and download EDIUS and give it a go with it's Canopus HQ codec. It has real good CC and slow mo and encoding out all different formats is a snap. I did a clip the other day mixing HDV and DV on a HDV timeline with effects all in real time. Rendered out a DV file from it and firewired it back to the cam as DV.
O what fun 
