Simon -
the levels on the 302 are calibrated so that 0 VU = 0 dBu. But the max output (for the "line out") is +20 dBu. and the meters go up to +20dB.
For line-in on the 722 (at 0 dB gain), the 722 will hit 0dBfs with a signal level of +20 dBu.
This isn't too surprising, as both these products are SD, and they have been designed to work well together.
so running line-in on the 722, with 0dB gain, the meters on your 722 should match the meters on the 302. so just adjust the 302 as necessary, and leave the 722 levels alone. It shouldn't matter which set of meters you are watching, because they'll both be the same.
- Jason