[Legolas]

One thing you could try is bashing it with a missile weapon. It helps if you use ammunition which deals elemental damage when you do so. Area of effect spells like Fireball, or certain specific ones like Ray of Frost and Flame Arrow may work as well.
However, the chest may be invulnerable to damage entirely.

In that case, you'll need to use a Find Traps spell or buy Thieving Tools. Alternatively, get a rogue for a henchman or use a pixie familiar.
In the event that the DC is still too great, triggering it is indeed the only way to disarm it. You can do this with possessed familiars, or indeed with characters under the effect of Constitution buffs, granted Temporary Hitpoints and under the effects of an energy protection spell. If you're desparate to get at it, die and use the respawn option.

Still, some traps won't disarm after being triggered. If you're facing one of these stuck on an indestructable chest, you need someone with a good disarm skill around.