Do I really need a preamp?

Any input impedance is "compatible" ie it will work. Its more a question of how well. The 10X rule is commonly cited. That's a reasonable approach, the challenge being that impedance can vary widely at different frequencies and a single output impedance rating may not reflect the worst case, so I think it best to include some tolerance as an insurance policy whenever in doubt.

47Kohms is most likely a good match in general. I would not be concerned at all if everything else looks good. I cite 60kohm merely as a very safe number to go by in most any case based on what the vendors seem to commonly go for when designing towards the goal of compatibility with tube pre-amp gear. Higher input impedance is pretty much always as good or better for best results in regards to low distortion, detail and dynamics.

YES it is the heart of your system

We really ask alot of that litle potentiometer in that preamp of ours. We put the whole audio signal through it and ask it to attenutate just what we want, just the way we want it too. We want it to bring us the emotion, without any distortion. We want to be able to hear the quiet, and unravel the loud. That is a tall order and you really (REALLY) need a higly resolving preamplifier (unless you have an aeris, etc, ie a dac that has some real archectecture behind the volume control)to pull it off. Some live perfomrances can benefit from a good preamp.

every time I have tried a Dac with a volume control, it did not sound as good as having an actual preamp in the system. Granted, I have only tried it twice, but as others have said it would depend on the system. of course these days there is DAC/peramps and Preamps with built in DAC, Intergrateds with DAs ect.. Lots of options and many ways to get the sound you want.

I use a passive attenuator. I see George saying what matches well with such a control in a system. I would like to say that I think in my system I benefited from a source that has a more robust power supply in it. Not more volts output, but a larger supply. But I don't know why. But it sounds better than a very similar (moon d100 v moon d300) source with a smaller power supply. I can't say for sure but I think the power supply might be largely responsible for a more natural, noticeably fuller, less lean sound. It has me thinking that everything in a system effects how that passive works out well or not. To a larger degree than a system with a active. So maybe after you get the full signal to the amp with the least amount of electronics in the path of it, it can show it's magic.