This is a case where the Mackies inserts are operating at +4 operating levels, and you are using the -10 inputs on the ADAT's, which would mean that that ADAT is seeing about 12dB more gain than it really wants to.
On ADAT's, the only way to get +4 operating levels is to use the Elco connection, which is by the way balanced (your inserts are unbalanced, but really, running the unbalanced to the balanced connection should not pose any problems....).
In line pads will solve the problem, but at the expense of running a transformer in-line. If the transformer is very high quality, like a Jensen, this will be mostly unnoticeable to your average set of ears. But a cheaper transformer is going to create phase distortion starting usually around 13-14KHz. You will notice that the sound is somewhat less open sounding.
Really, a line matching transformer is not a great solution. Those are great for when you have an emergency and need something to get you by. But for the long term solution, you really need to match you operating levels between the console and the ADAT to assure the most pristine, clean sound. An acceptable Elco cable and patch (both used) should cost you less than $200.
Good luck.
Ed
