Hypersonic Assault lets Tachyon pay a health so that her next Attack Roll uses dice equal to her Move value.
Lightspeed Barrage lets Tachyon apply an Active Attack on all the of the enemies she passes through. Let's say she has a Move of 6 right now. Now she pays a health to use Hypersonic Assault. Then she uses Lightspeed Barrage to pass through a Turret, a Pylon, and Baron Blade. Lightspeed Barrage lets her make an attack and target every enemy she passed through. She chooses Nimble Strike, and because she paid a health for Hypersonic Assault, she rolls 6 dice, and applies this attack to the Turret, the Pylon, and Blade. Is that right? If so, it's a great way to demolish things in BB Scenario 3 :) OR is this handled like Aim and area attacks, where the Aim only applies to one of the targets?
Since she's making one attack on multiple targets, and Lightspeed Barage changes the dice on her next attack, it changes it for all targets. If it had separated and made an attack on each different target, you would only get to apply it to the first target you damage.
For me this just brings up the question of "Does she hit all those targets with one attack, or does does she get to attack each target she passes through?" ie. is it a new attack for each target regarless of the fact that it is one action. I currently don't have access to the cards to check the wording on lightspeed barrage, but it probably isn't difficult to check.