One of the new features in the Canon T3i lets you select full Manual Audio, dial down the in-camera pre-amps, and go all JuicedLink DS214 with headphone monitoring. Damn this is so much easier than all the other random ways to control, monitor, and route incoming audio into DSLR's. If you still liked running a Dual Audio system, you can run a Zoom H1 or H4n on the output between the camera and DS214.
You can see the relative size of JL's DS214 next to the Canon T3i and Rode VideoMic Pro, all mounted on a (gratuitous product shot) of the Juicedlink Accessory bracket. It's such a simple looking setup, but you've got control over the Rode VideoMic with -10db, 0db, and +20db, and then you have a Low / High Gain features in the JuicedLink DS214, along with incoming Right and Left Levels adjustment, and finally piping that into the T3i Manual Audio controls...
Doesn't look like it in photos, but this thing is small. The DS214 is really a great little device to professionally (and simply) add headphone monitoring and level adjustments for microphone inputs to DSLR's. The DS214 even includes AGC Defeat so this little black box can literally work magic for all DSLR audio shortcomings. Love the starting price point too. I'll mount it up next to a camera and show what that would look like.
Ok, so you got your DSLR and fancy new Rode VideoMic Pro with +20db feature. If you've got AGC on the T2i (without ML) or Canon 7D, then you need a way to disable AGC. Or maybe you don't? Maybe you've got a Canon 5D Mark II or 60D with Manual audio levels - no AGC to worry about. You're still short of a way to monitor the audio levels via headphones.
There's been different ways of trying to get clean audio into your camera, but it normally came at a hefty price. Here's where this new JuicedLink DS214 comes in. Just recently announced as available for purchase for under $145 bucks, this little black box provides all the missing features of running a stereo jacked microphone into your camera. The DS214 provides you with Audio meters, a Low-Noise Preamp, Headphone monitoring, and even AGC Disable if needed (everything that sucks for a DSLR). Ok, yes you can use an MP3 player with constant tone to 'tame' the AGC, but still no way to adjust levels from the Mic, or give a little low-noise preamp boost to the signal. Any way you cut it, this thing was thought out to include all the different 'workarounds'. For the price and convenience, it can't be beat.
This version doesn't have inputs to support XLR Microphones, but there's a swamping new audience using the Rode VideoMic Pro that sure could use something like this. For XLR phantom power you'll want to check out the DT454. Only 1 stereo input? The DS214 also has seperate L/R potentiometers which makes it possible to run a splitter to two different mics and capture mono on each channel.
As of now the new JuicedLink DS214 is only available on the JL site with a bunch of information which I suggest you checkout to see if this will work for you. There's also some different Audio Samples from a variety of possible Audio setups with the Rode Mic + Zoom H4n you can listen to.