Yes, DR2d allows you to record two external stereo inputs, for 4 channels total. To do so, set the recorder to DUAL LINE mode.
You will need an external powering solution for the mics into the LINE IN. Line in gain can only be adjusted in the menu prior to recording. Usable range of gain on LINE IN is only between 95-100. Do not go below 95, there is no benefit and only potential problems. For those reasons, a preamp with adjustable gain is highly preferable to a battery box going LINE IN. If you don't have a preamp with adjustable gain, plug your preferred mics into MIC IN. If you do have one, use your preferred mics through it.
Plan A) Best strategy is using two preamps with adjustable gain, one for MIC IN, one for LINE IN. If using two preamps with adjustable gain, set input gains to MIC IN (LOW SENSITIVITY) = 67 and LINE IN = 95. That makes input sensitivity effectively equal for both inputs, and maximizes available headroom. Turn plug in power (PIP) off on the recorder.
Plan B) If using only a single preamp, use it for the LINE IN pair (input gain set to 95). Use MIC IN for the pair that does not have an external preamp and set gain as needed on the recorder. Plug in power (PIP) is available for MIC IN on the recorder (menu switched). You will also need to check that MIC IN sensitivity is set appropriately, most likely to LOW (choice of HIGH/LOW). If you have a battery box in addition to the preamp, uses that for MIC in instead of PIP power on the recorder.
Plan C) If you have no preamp but two battery boxes, use them both and turn PIP off to MIC IN. Set MIC IN gain as needed on the recorder. Keep in mind you cannot adjust LINE IN gain while recording, AND the available range of input gain is very limited. Good luck.
Plan D) If you have only one battery box, you'll need to use that for the line in pair. Use PIP on the recorder to power the MIC IN pair and adjust gain as needed on the recorder. Good luck.
You can switch the meter monitoring between MIC IN and LINE IN while recording, unless the HOLD switch is engaged. To use the IR remote you'll need to first enable it in the menu. The IR remote remains operable with the HOLD switch engaged.