Variant Channeling: Undeath + Undead Lord. Does it stack?

[MrNormal]

This thread is pretty cut and dry; does something stack and how. RAI or RAW.

1) Undeath: Heal—This works like a standard channel (not halved). Harm—The healing effect is enhanced for undead creatures and those with negative energy affinity.

2) Some variant channeling abilities are enhanced when used on particular creature types. Such channeling increases the normal healing or damage from channeled energy by 50% for that creature type, rather than the default half healing or damage for the alternative channeling

3) Unlife Healer (Su)
At 8th level, the undead lord’s spells, spell-like abilities, and supernatural abilities used to heal undead heal an extra 50% damage. At 16th level, these effects automatically heal the maximum possible damage for the effect + the extra 50%. This does not stack with abilities or feats such as Empower Spell or Maximize Spell.

Obviously it's about channeling negative energy. Since it's a variant and not an ability or feat: does the added negative energy from the variant channeling stack with the added negative energy from the class feature?
Do we call it an ability and limit the optimization to 150%? (it doesn't stack)
If it does stack, does it multiply or add to itself? 100% + 50% + 50% = 200% or 150% x 150% = 225%
And lastly; does it all maximize at 16th level?

Discuss.

[Saethori]

Everything functions off the base dice rolls. You apply bonuses additively, not multiplicatively.

So, before 16, your negative energy channels heal undead for 200% of normal. You roll Xd6, and then double it.

For example, you roll 5d6 at level 9. Then, the result is doubled to determine how much it heals undead.

After 16, your negative energy heals for maximum and a half, plus 50% of the rolled value. So you roll Xd6, halve it, and then add 1.5 times the maximum possible result of the channeling dice.

For example, you roll 9d6 at level 17. You halve this value, round it down, then add 81 (1.5 times 54, the maximum result), to determine how much you heal undead.

[Ashram]

Technically, Channel Energy is a supernatural ability. Since I'm almost positive that there's nothing that says otherwise (Since this isn't like metamagic stacking) the two effects would stack, but only as additives and not multiplicatives (AKA 100% + 50% + 50%). And then at 16th level it would be like maximizing and empowering your channel (Max + Half max)

[master_marshmallow]

Saethori wrote:

Everything functions off the base dice rolls. You apply bonuses additively, not multiplicatively.

So, before 16, your negative energy channels heal undead for 200% of normal. You roll Xd6, and then double it.

For example, you roll 5d6 at level 9. Then, the result is doubled to determine how much it heals undead.

After 16, your negative energy heals for maximum and a half, plus 50% of the rolled value. So you roll Xd6, halve it, and then add 1.5 times the maximum possible result of the channeling dice.

For example, you roll 9d6 at level 17. You halve this value, round it down, then add 81 (1.5 times 54, the maximum result), to determine how much you heal undead.

Is there a citation for this?

[Saethori]

Maximize Spell wrote:

An empowered, maximized spell gains the separate benefits of each feat: the maximum result plus half the normally rolled result.

While I cannot find anything more exact than this while on my phone, many other effects in the game encourage additive bonuses.

Basically, you apply every feat and every bonus individually.