I'm totally overheated right now, I have the feeling I don't understand anything about audio anymore. Please help me.

1. I tried to record from a condenser mic onto a marantz pmd 670 with a sound devices 302 in between the two. But the audio was incredibly noisy. Also when I record straight to the Marantz 670 I get a lot of noise in the background. If I don't record to the Marantz but just listen to what the Sound Devices outputs, I also get a lot of hiss, and there's not much input from the mic that I can see on the leds (48v is on).

2 Same problem with my xh a1, incredible noisy sound. Made a few films with it, and I just recently noticed the noise when I listen to the audio output of my camera. Is that normal?

3 What was it again about the final mix of a audio track? It is supposed to be between -9 and -12dB right? Because when I play that back on a tv, the audiolevel is incredible low.

Thanks in advance.

What sort of condenser mic, what are you recording (speech? music?) and how far away is it from the desired sound source? Try this experiment - on your 302 plug the mic into Input 1, set the sensitivity switch to 'mic.' and plug in a set of phones. Set the Channel 1 fader to the midpoint of its range (mark pointing straight up), Pan switch to 'center'. Select 'PFL 1' on the headphone select switch. Have someone speak into the microphone at a normal volume from about 12 - 18 inches away, and adjust the Channel 1 Gain control (DO NOT adjust the fader, use the popup gain trim knob instead) until the meter hovers around the "4" LED on normal speech. Move the headphone switch to 'Stereo', adjust the headphone volume to a loud comfortable level, and see if the hiss you're noting still remains.

Ivo, has this worked for you?

Yeah, it sorta worked out. I discovered that there's a lot of strain on the combinations you make. The microphone was just not perfect for the mixer. But the tips I got were enough to get decent sound out of the mic.
Some time ago I tested the sennheiser k6 with me66 on a marantz pmd660 and it worked great.