Hmm, let me do a bit of math here, but I think you'd be a tad off because you're not calculating both weapons early on but using a Dual Power Attack, which also would require an additional set of calculations because you're going to be hitting more than once and doing 'Power Attack' damage rather than just a regular attack which again should add another level of math to the whole thing.
Also, you've slightly confused your sneak attack damage. Backstab is replaced by Assassin's Blade when considering Daggers and only really effects Swords/Axes/Maces from then on. So here you'd only have a 15x boost rather than a 6x boost and a 15x boost.
So, if we're looking at this with those factors as well (and do understand that I'll probably have missed something).
First: You calculate the base damage boosted by Armsman 1/5
9 times 1.20 + 11 times 1.20 = 10.8 + 13.2 or 24.0 damage
Second: You calculate the effect of a Dual-Wielding Power Attack (1.5 damage, also is 3 attacks).
(24 times 1.50) times 3 = 108 damage
Third: You calculate the additional damage of Dual Savagery.
108 times 1.50 = 162 damage
Fourth: You calculate the additional damage of Assassin's Blade
162 + 15 = 2430 damage for a Dual-Wielding Power Attack.
So yeah, slightly different math but you can see the relatively large difference. You'd even get an extra boost from ah, the Dark Brotherhood Gloves of various nature, where you'd do 30x sneak attack damage rather than 15x. So yeah, hope that helped a bit mate but the answer I suppose is, yes, Armsman boosts your damage.
Hmm, let me do a bit of math here, but I think you'd be a tad off because you're not calculating both weapons early on but using a Dual Power Attack, which also would require an additional set of calculations because you're going to be hitting more than once and doing 'Power Attack' damage rather than just a regular attack which again should add another level of math to the whole thing.
Also, you've slightly confused your sneak attack damage. Backstab is replaced by Assassin's Blade when considering Daggers and only really effects Swords/Axes/Maces from then on. So here you'd only have a 15x boost rather than a 6x boost and a 15x boost.
So, if we're looking at this with those factors as well (and do understand that I'll probably have missed something).
First: You calculate the base damage boosted by Armsman 1/5
9 times 1.20 + 11 times 1.20 = 10.8 + 13.2 or 24.0 damage
Second: You calculate the effect of a Dual-Wielding Power Attack (1.5 damage, also is 3 attacks).
(24 times 1.50) times 3 = 108 damage
Third: You calculate the additional damage of Dual Savagery.
108 times 1.50 = 162 damage
Fourth: You calculate the additional damage of Assassin's Blade
162 + 15 = 2430 damage for a Dual-Wielding Power Attack.
So yeah, slightly different math but you can see the relatively large difference. You'd even get an extra boost from ah, the Dark Brotherhood Gloves of various nature, where you'd do 30x sneak attack damage rather than 15x. So yeah, hope that helped a bit mate but the answer I suppose is, yes, Armsman boosts your damage.