Hey KOMSAT, you could try a Type II Chrome Cassette...more overdive headroom and much cleaner sound...the metal Type IV cassettes are better but too expensive ,not good value for money...However the TDK was my favorites one(I've tried almost all brands that where available at my country and the worst where the Type I sony made)

I always wondered what sort of sound the different tapes would get you. Good to know. I don't actually own the WM D6c right now but I'm looking to purchase one in the next week or two.

The main difference is the SNR(signal to noise ratio)...I mean better quality tape=less hiss...but when you push the input levels then saturation depends &on the type of the tape..However the tape recorder must support type II tapes(it's usually written on the tape recorder).

I kinda like the hiss...haha. I use it more like an effect, the compression, overdrive and tape hiss together are great on drums. Still I'll have to try some more professional recording methods and see if it does anything for me.