Do you have an iPhone or Android? If you do you can download a free SPL meter and then group the outputs once you have calibrated the speakers.
The SPL does not need to accurately calibrated it only needs to be consistent.
If you are careful you can also use the 003 to calibrate the speaker levels.
Generate sine waves at different frequencies and then replay them through the loudspeakers separately. Use the same mic and preamp/channel to record each speaker and then use the Gain in AudioSuite to establish the RMS and peak levels. With a lot of patience you will be able to match the levels on all three loudspeakers as well as be confident about the frequency range and balance.
Let us know how you get on.