1) Start out with the recorder's level set at the recorders' unity gain setting. I know nothing about the DR 2nd, but the R09HR's unity gain is around 38-40. Setting an HR at -12 and bringing up the levels to the -12 to -6 dB range with the CA-9200 is a huge mistake. The recorder's levels will look fine, but you will have to crank up the CA-9200 so high that there's a good chance you will likely cause Ca-9200 itself to to clip and you will never know it until you listen to the recording (or are monitoring with headphones). Never set any recorder's levels way below unity gain and bring the levels way up with a preamp.
2) What you set the CA-9200 to depends on how loud the band is, but unless the band is excruciatingly loud you can normally start out by setting the CA-9200 to +25 dB with the output knob at 100% (since the 4.7 mod reduces the output to the recorder by approximately 10-12 dB). As long as your recorder is set to unity gain, the meters on your recorder will tell you if you need to raise or lower the CA-9200's gain setting. If you don't get adequate levels at +25, try +30 and if still not adequate +35. If the meters don't indicate going over - 0 dB, your recording will not be clipped. However, if you set the R09HR well below unity gain, you can easily get a clipped recording even though the recorder's meters stay below 0dB. You can also make minor level adjustments down with the CA-9200's volume control. Just don't make major adjustments with the volume control to keep the levels from going over 0 dB or again you might cause your CA-9200 to clip and the recorder's meters won't warn you.
I've recorded a fairly loud (but not super loud) band with the following settings: AT853's (Cardioiods,) > mini-XLR CA9200 (4.7 mod on) set at +30 with the volume control eventually turned down to 75% > Edirol R09HR set at 38 with the mics about 10 feet from the band's speakers. I got a great sounding recording with peaks about -3 to -5 which is a little closer to 0 DB than I prefer to be. It would have been safer to have the CA-9200 at +25 dB (and turn the volume control down a little bit if necessary).