I've used LibertyX with Cash in combination with Grams Helix and the results were fine. But I was wondering, is there any real reason to use cash if I'm going to tumble and get fresh bitcoins anyway? Buying bitcoins is legal, after all, and I'm sure tumbling them is too. Is the cash part just excess if tumbling as I suspect or is there something I'm missing? Thanks!
If you are confident that your privacy is not compromised during or after tumbling, it should not be detectable what method of payment was used. More accurately, the coins purchased on a card should be just as untraceable as coins purchased with cash, if the tumbling is private and effective. That could be a big "if" though, as it consolidates the trust to a degree.