I have run Nak 300's > R09 mic in, with just a Y cable. It works, but I had to max out the gain on the R09, so hiss starts to be come apparent, and the sound is kind of "lackluster" for lack of a better term. If you can find some of the Hosa Low-High impedance transformers that might help, but a "real" preamp is the way to go.
The original old school Nak preamp is the MX-100. It's a 3 mic mixer, but it works fine for 2 mic preamp as well. Set the R09 to about mid gain, line in, and adjust the gain on the MX100. It's kind of a brick, but I've seen them for a bit more than $100, modded to run on 9V batteries.
I've had great luck with UA-5's. They are primarily digi out, although you can use a UA-5 analog out. This creates kind of a confusing setup because there are 3 different places you can set the gain... (a) the main knobs, (b) the headphone volume which effects the analog out the back, and (c) the gain on the R09. Many people who try this end up putting too much gain one place, and not enough on another... and it doesn't sound as good as it should. If you want to use a UA-5, talk to Vanark... he is one of the few people I know who run mics > UA-5 > R09 a lot, and he makes good tapes, so I would say he has a routine figured out.
I've had great luck with a V3... but you probably aren't looking to spend $900.
The Nady DMP-2 is one I don't really recommend. Since you have to crank the gain up on the preamp it's about has hissy as running Mic-in to the R09.
Silly as this may sound... if you can find someone who has an old Sony D5 analog cassette deck, that makes a great preamp for the Naks... run Mics > D5 > R09... I haven't done it, but I've seen it done. I think you just leave the D5 on Pause all night.