Do I really need a preamp?

Its all about synergy as usual I think. Passives make sense to me if properly mated to suitable sources electronically. That might even be one of the best ways to go if done right, at least from the "purist" point of view, a simple signal path that mates well to gear upstream.

What's not to like?

Mating of active pre-amps, especially tube gear, opens up a similar but different can of electronic mating issues to address. Plus the preamp itself becomes more of a potential sound tweak.

There are so many ways to tweak and do it right. Active/passive, who cares really? Just choose your paradigm and do it right! Passive pre-amps offer a different way to do things. Options are good. Just get it right.

When researching SS amps to go with my current ARC tube pre-amp, I found a surprising # of leading contenders otherwise with 10Kohm input impedance or not much higher, especially older models. The trend in more recent years might be different,perhaps due to popularity of tube pre-amps with audiophiles.

Most that mentioned design for use with tube pre-amps tended to be in 60-100kohm range, unbalanced, double that for balanced.

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.