A little tweak to these armors. I like them, but they're sadly very rarely considered even for lower level play due to how they're designed now. Which is sad, because there is an entire resource in the game dedicated to crafting these items. They are a significant investment to craft as well, requiring 300+ crafting points.
The shield and helmet are fine as they are now, as they're essentially mithiral armors that are circumstantially better than adamantine against slashing damage. Aka; the most common type of damage.
The armor and gauntlets aren't in a good spot right now:
Ankheg Gauntlets: 10/- Acid DR, 10% Acid DR. No stat or skill bonuses make this a poor choice compared to even low level basin gear.
Ankheg Breastplate: 4 AC chain armor with +2 AC, 50% Acid Immunity and +5 vs Poison. Not terrible, but it looses the AC vs Slashing bonus the shield and helmet get. A save vs poison is a little weak, as poison typically isn't going to be an issue for most characters after a certain point due to high fort saves or available healing resources.
Warded Ankheg Breastplate: 5 AC breastplate with +2 AC, 50% Acid immunity, +3 saves vs acid and +2 universal saves. Decent save bonuses but worse than the breastplate as armor, as the max AC this can give you is 9 with DEX, whereas the breastplate can give you 10 with dex.
Most of these seem to be geared towards defending against acid, and I vaguely remember Mestils acid sheath being a hot issue around the time these were implemented. Outside of that very specific instance however, high levels of acid damage are pretty rare outside of traps or very specific creatures, which dramatically cuts down on these armors utility.
Suggestions to make these items better?
Gauntlets - Add a +2 CON boost and maybe a few skill bonuses. Drop the acid DR slight to 5/- to comphensate. Or remove it entirely. Maybe make a second runic version of these as well?
Ahkheg Breastplate: Give it the +4 AC vs slashing (hell, even a +5 vs slashing to keep it competitive with high end gear) and let it be treated as light armor, similar to elven chainmail. Ahkheg shells were strong, but significantly lighter than metal (source; BG1)
Warded Ankheg Breastplate: Make it chainmail instead of a breastplate, give it the same treatment as the regular breastplate, but throw a runic property on it as well. Drop the acid immunity slightly and you can probably change the acid save to something else.