Ok, me then. The 5% DCI works for everyone who equips the quiver, archer or not - that we know for sure. But the other thing about the 10% Damage Modifier...
The question whether magical quivers modify the damage of non-archer weapons has been asked before. Frarc, me and others tested a bit around and we found no difference, but that's not an evidence because the overall damage varies too much that you could conclude from that if the Modifier applies or not. Normally they shouldn't - for obvious reasons. I found no affirmation for either way in the past FoFs. IMHO, they don't. For testing, I took on a Quiver of Fire which gives you both 10% Damage Modifier and 50% Fire Damage. Slashing at Ice Fiends with a normal sword I found out that taking on/off the quiver doesn't seem to make any difference - quite contrary to using the Consecrate Weapon spell. So...
Edit: Maybe you ask this in the
Warrior section again for more answers.