Scenario: Possession tradition character with 6 in all stats summons, binds, and invokes a force 10 spirit with an arbitrary number of services and 6 hits on the Invoking test.
Questions:
1.) What does the resulting merged character's stat line look like?

a. Does the Invoking metamagic increase his merged physical stats? (E.g. all physical stats at 17. 6 base summoner, +10 spirit, +1 from 6 hits on Invoking test.)

b. Do the spirits higher mental and special stats override the summoner's for the duration of the possession? (e.g. mental and special stats at 10?)

2.) If the summoner's Magic is increased,

a. Does he use his new Magic value of 10?

b. Can he cast a spell at Force 20?

c. Does he use his new mental attributes of 10 Willpower and 10 Drain stat to resist?

d. Can he additionally spend an Edge point to add an additional 10 points to the test?

3.) If the summoner's Edge is increased,

a. What happens if the character spent Edge points while possessed but later releases the spirit, how does this affect the character's current Edge pool and how does it affect the spirit's pool?

b. How does permanently Burning Edge points affect both the summoner and the spirit?

Hm... my opinions:
1.
a. Sure... explicitly stated in the rules: p 57, Street Magic. Possession spirits get it too.
b. doesn't matter if they are lower or higher or anything. The spirits mental attributes are used.
2. (The summoners magic gets overwritten by the spirits force)
a. Yes, but no. HE doesn't do anything with the new "force". He just commands the spirit.
b. Nope... because he can't cast anymore. The Spirit may (if it can use its innate spells and powers at that level). Also i don't think spirits like to overcast... maybe if you ask nice.
c. The Spirit... yes.
d. If it REALLYREALLYREALLY likes you... MAYBE... but unlikely.
3.
a. when the spirit leaves you are yourself again. Your edge etc. should be untouched.
b. THAT a spirit will never do for you... hm maybe your ally spirit...

So my point is: you don't just get some buffs. You can watch and direct the spirit... but the Spirit uses your body. You yourself can't cast anymore, or do anything. The Spirit doesn't get your skills, your knowledge, nothing.

Unless you have Channeling. Then you get some buffs.

Note that Possession is still limited to Augmented Maximums, so you won't be getting 17 in every stat

Wait... so putting on a mechanized suit of armour ignores augmented maximums (by way of external servo-motors) but putting on a force 10 spirit doesn't (by way of external magic power)? I don't like that. Stat increases from possession seem to have nothing to do with the character's physique.

Only Strength can be enhanced by powered armor. Possession enhances all four physical stats.

Even if that would be true (OH how i hate hardcaps on stats grrrrr) wouldn't it be that YOU are the supplement or bioware for the spirit? I know it is said, the force gets added to your stats... but i reckon IF this cap is true, wouldn't it be 1.5 time the spirits attribute? Just to be fair?

Also: DOWN with the arbitary limits... BOOOOH.

No. The spirit is possessing your body. Thus, it is your body being enhanced. It's impossible for the spirit, no matter how high its Force, to lift a 5,000 ton object with your body because your arms would rip from the sockets if it put its full strength into it (as an example).

Thanks for the reply, Summer, because that's a different insight into the scenario than I was thinking regarding Channeling. I was approaching it as if you had total control, but it does seem to be more of a shared control. I was basing the idea of having full control with Channeling off of this quote from The Possesion FAQ: "2) If a mage with the Channeling metamagic ability possesses himself with one of his spirits, can he wield magic?
A: Yes, the mage's special attributes override the spirit's special attributes and the mage can cast spells, conjure spirits, enchant objects, etc. (Otherwise, there is no point for Channeling.) The mage uses his own Magic attribute (not the spirit's)." I actually don't see textual support for the FAQ claim but I didn't search the whole thread for reasoning. The text in Street Magic all seems to indicate that your mental and special stats are overridden by the possessing spirit regardless of whether you have Channeling or not. But that would seem to make spellcasting while possessed impossible outside of commanding Spirits of Man to use Innate Spell, which doesn't seem to be the intent.

I'm now thinking that the answers to my questions are:
1a.) Yes, physical stats are 17.
1b.) Yes and no. Yes the spirit has it's own stats when you get it to do something with it's own abilities (spirit powers, potential skill use, etc.) but not when you use your own abilities (your own mentally derived skills like First Aid, abilities such as spellcasting, etc.) In those cases you don't use the Spirits mental or special attributes, you use your own. Which basically answers all of 2 and 3. And for passive events (such as resisting spells) it is clearly written that you use the lesser of the stats between your own and the spirit's.

Thanks for redirecting my thinking.

This is incorrect. You are not limited by your racial augmented maximums while possessed. By RAW I don't believe there is any limit, but the Official Shadowrun 4 FAQ states:

The possession-aug-max thing was pointed out to me by one of my players playing a possession tradition mage. I didn't think it worked that way either, but he pointed me to a specific, unequivocal sentence that stated that possession was limited by aug max. I can't find it now in my copy of Street Magic; I'll see if he remembers where exactly it was.

Zurai, your friend was wrong. The info from dirkformica is correct.

I'm pretty sure one of the devs (Synner?) mentioned that the augmented max DOES apply to possessed individuals in a thread a couple of months ago.
Can't find it right now.
Of course this was before SR4A so it might not apply any more.

He also might have said that he thought it SHOULD apply. Synner talks about rules design a lot, and it's easy to misunderstand him.

Note that it isn't: You add the spirit's force to your base stat to recalculate the new Augmented Maximum.