On Pc/NA if that helps. Anyways, the 5-piece bonus of the Soulshine Set is to add 450 Spell Damage to cast-time and Channeled abilites (Well 450 if all pieces are at gold quality)
Magicka Detonation and its morph Inevitable Detonation both have a cast time of 1.5s But arent effected by this bonus whatsoever as far as I can tell via the tooltips in game.
I'll attach a few potato quality screenies of the tooltips, but to be honest the difference between the first pic, and the second damage wise is due the piece of the soulshine set Im removing is an Infused magicka Chest piece. wtih a little over 1k magicka bonus on it.

Heres the pic with the 5-piece of soulshine active, but the only damage bonus Im gaining is from the boost in Magicka from the enchantment on my armor.

And heres the tooltip after I take that piece off, once more, damage reduction is due to the lose of an infused enchantment on a chest piece.