Never stop shooting + Diehard + effective constitution score

[Calel101]

I think I am posting in the right place (correct me if I am wrong).

If a character has the never stop shooting trait:

Never Stop Shooting:

If your hit point total drops to 0 or lower but you are not dead, you may act as if disabled rather than dying (as if you possessed the Diehard feat). However, you can use your actions only to draw a firearm, reload a firearm, or attack with a firearm. If you have the Diehard feat, this trait also allows you to substitute your Wisdom score for your Constitution score for the purpose of determining the negative hit point total at which you die.

And also has the diehard feat.

If the character attain any effect that modified their "effective constitution for determining when a character dies" or similar verbage; such as

Lingering Spirit Discovery:

The alchemist is familiar enough with the ties between his body and spirit that he lingers at death’s door far longer than a normal person. He treats his Constitution as 10 points higher than normal for the purpose of determining when hit point damage kills him (so an alchemist with a Constitution of 10 and this discovery dies at –20 hit points instead of –10). Reducing him to 0 Constitution or its equivalent (from ability damage, ability drain, Constitution penalties, and so on) makes him unconscious and comatose, but he is only killed after taking an additional 5 points of Constitution damage, drain, or penalty (in effect, the alchemist must be brought to –5 Constitution in order to be killed by these attacks).

OR

Tourmaline Sphere:

This stone grants you a benefit only when you're dying. When determining the number of negative hit points you must accrue to die, treat your Constitution score as if it were 2 higher. This doesn't provide a bonus to Constitution, so it doesn't grant a bonus on checks made to stabilize but does provide you 2 additional rounds during which to attempt such checks. You can only benefit from one tourmaline sphere ioun stone at a time.

Does this change how deeply negative a character can go before dying based on the substitution of their wisdom score, or does it only count from their actual con score.

Example:

I have never stop shooting trait and diehard. I have CON 8 and WIS 16.

I buy a tourmaline sphere.

A) Do I die at -16 (sphere doesn't help)? or -18?

B) Also do these "treat CON score as ____ higher" stack?

Thanks for any feedback, and sorry for the convoluted question. Hope I expressed it clearly.

[Bart Vervaet]

A) I'd say -16. both abilities speak specifically about your CON score.

B) Seems like they are both untyped bonuses, so I think they stack. If you have both the discovery and the ioun stone and a CON of 10, you would die at -22.

[Paladin of Baha-who?]

If it said you die at -Wis instead of -Con, you couldn't affect it, but it says you can substitute your con with wis, which means that anything that affects con for that purpose now affects wis for that purpose instead.