I've said it before and I'll say it again, copied from another thread:
1) Unless you have some ludicrous amount of Willpower promotions that you're literally one-shotting everything you come across, Power Chord spamming will run into mana issues. You need to weave in animation-cancelled auto-attacks in between to charge your mana here and there.
2) The armor buff song is far and away the most mana and time-efficient defensive buff for most of the situations you'll encounter. Take the song duration upgrade passive, and you get an immense survivability boost against physical damage for 12 seconds. Cast it once before you dive into a group of enemies. You will notice the difference in incoming damage.
I would actually go so far as to say that the Barrier song is very, very rarely worthwhile in comparison, especially since all Barriers got nerfed awhile back. 20% Barrier is a total trap. Why? Because it's horribly mana inefficient, it begins decaying immediately, and armor is not taken into account when you have active Barrier - no matter how much or how little Barrier you have. That last factor is key, because it applies to carryover damage that gets through your Barrier.
Let's say you have 10 points of Barrier when you take a swing that does 200 damage. It wacks through the 10 points of Barrier, which means there's still 190 points of damage - and that still uses the Barrier damage reduction calculation (namely, you get none.) You take that 190 points of damage straight to your health. In comparison, if you'd taken that blow on 170 points of armor, it would have reduced it to 30 points of total HP damage. (Yes, I know the damage formulas are slightly more complicated, this is just an example.)
Unlike the Keeper or Saarebas, who give large amounts of Barrier at a time, the Virtuoso is relegated to giving small chunks at a time, and is mana-gated. Because of how rapidly Barrier decays, a Virtuoso casting that song on people is far more likely to create situations where enemies hit a target with minuscule amounts of Barrier, and thus hit for artificially inflated amounts of damage against the party.
Barrier Song is a trap. You will boost your party's survivability far more with the armor/resist buffs, with far greater time and mana efficiency.