[Grimmly Fireforge]

All Bard instrument modifiers are working as intended.

McVaxius' Horn of War increases the damage of of your Denon's Dischord song by 140%.

A "Horn" that you buy from a vendor increases your Denon's Dischord damage by 110%.

The difference between the two is not going to be huge. And remember that other things factor into your Denon's Dischord damage. First of all, your damage output is going to be capped by the level of your Bard and the level of your Brass Instruments skill as well. You may not see the full benefit of a McVaxius Horn until mid-to-high-levels.. And like I said, it's not going to be a HUGE difference.

Also, equipping a horn doesn't increase the radius of your Denon's Dischord, or make it less resistable, and it doesn't make Denon's last more ticks. All it does it increase the damage of the DoT per tick.

I hope this was helpful.