Imperial stout stuck ferment

Scenario:
21 lbs of grain, 5 gallon batch, American Ale yeast with a starter that was too small. After 10 days of 68-72 degrees I took a gravity reading and got 1033. It stopped bubbling 3 days ago and as of last night the krausen had expired. My OG was 1098 and according to some calculators (online,ken powers) the FG should be 1025.

17lbs 2 row
1lb crystal 60
.5 lb chocolate malt
.5 roasted barley
1.5 oats
4 tbs of hersheys cocoa (dried for baking)

Is it possible that it did ferment all the way and that the unfermentables have thickened it a bit?

Should pitch another yeast starter? Champagne yeast? help.

I'd say the yeast has given up. Rack it to a secondary and pitch some champagne yeast. Give it a month or two. Ales that big can be slow to finish. I like to pitch my barleywines on the cake from a brown or mild, but they finish slow anyway.

My bet is that it's done, not stuck. What was your OG? Does it taste too sweet?

The OG was 1098 and last night the gravity was 1031 (70F). If it is done than the ABV is only 8-9%, not dissapointed just shocked, I was shooting for 11-13%. It did not taste overly sweet but it is so young it is hard to tell. Is there any harm in pitching champagne yeast in the secondary if it is already finished? What about bottling? My plan is to rack it to the secondary add bourbon steamed oak chips (in a muslin bag I guess???) for 5 days and then pull out the oak and let it sit in the basement for 4 months, then bottle. Thoughts?

Sorry, I mis-read your original post.

Adding the Champaigne yeast won't hurt, and your plan sounds fine. I wouldn't be disappointed w/ 8-9% vs 11-13% anyway. It will probably taste better w/ the lower ABV and a little residual sweetness IMHO.

I say just let the primary sit for at least two weeks. There's no fear in autolysis yet. Just give it more time. Big beers take more time all the way around. By the gravity, I'd say it's close to being done, but keeping it on the yeast a little longer will be the easiest route.

I agree with most of the comments above. Off the cuff, Id say that to get 11-13% from a 1098, it would have to ferment down to drier than a popcorn fart.
My crasy impy I did was 1140 and only made it down to 1045. Thats about 12% and it is quite sweet. But drinkable IMO
As far as Champagne yeast, that was suggested to me when mine was at the stage and situation yours is in, I thought it a bit aggressive and too much of a departure frolm the plan that I was on so I just let it go and lived with it.
Agree again, not stuck, unless'n you call stopped a type of "stuck"
I'd say those numbers sound like it could be tasty. Call'er good and on your next similar recipe, just amp up your yeast factor in the equation. Bigger starter, higher attenuating yeast strain, more airation of the wort, etc.

If you compensate for the unfermentables, it looks pretty close to done. What was your mash temp?