I've done this a few times. I have a V3, an R09, and a buddy has an R09HR. What I used for a cable was an XLR > 1/8" cable I bought from sound pros, with no attenuator.
The V3's output is hot, so you end up turning the gain way down on the R09. On my older R09, down to like a 4 on the 0-30 scale. Another time we did it into my buddy's R09HR... I can't remember what the scale is on R09HR, but suffice it to say we were "most of the way down". At that point, for whatever reason, you get a result that is less than ideal. It doesn't contain obvious distortion, it's just not particularly sweet. In all of these cases, I was running the V3 "the way it is supposed to be run", i.e. I had the V3 running hot into some digital bitbucket, and I was setting the gain on the V3 to make the bitbucket happy, and the R09 was "the poor patchrat who gets what he gets".
I think you would be more successful if you do either of two things:
- set the R09HR line in gain to "midrange" and run the V3 "cold" as required to satisfy the R09HR.
- Use an attenuator, 20db, or maybe even 25.
I've been quite successful lately running my V3 > Korg Mr-1, where I made some 20db attenuator cables. At that rate, I can run hot into my bitbucket, and into the Korg simultaneously. I've not gotten around to doing the same with the R09, but I expect it will work fine.
I actually run into 2 recorders a lot... after the show my gear bag with the R4 goes in the trunk, and the R09/iRiver/MR1 is handy to listen to the show in the car on the ride home.