...and the award for worst sales pitch of the year goes to... Stomper!
hehe
I usually wear a really thin pair of cotton socks under my walking socks. This acts like an extra layer of skin and reduces any abrasion I'd normally experience from the rougher walking sock fibres. The cotton helps keep them cooler too.
From what your describing, and the fact that it's occurring on your descents, sounds like the little toes are suffering from increased heat/friction build up from your socks rubbing against the front area of your Manta's. May even be an idea to add another insole and tie your laces a little tighter round the ankles and towards the top area to reduce your feet from moving towards the toe-box of the boots.
You might have already tried these and have had no joy, sometimes our feet and certain boots just don't get along. As I've mentioned already in another thread. Mantas were a non-starter for me when I first tried them on in the shop.
By the way... what size are your boots that you might be selling with compatible GSB crampons?