Simple Q&A D&D 3.5 (by RAW) XXII

[Curmudgeon]

A 1597 No.

When he rages, his size category increases to Large.

While raging, a barbarian cannot use any Charisma-, Dexterity-, or Intelligence-based skills (except for Balance, Escape Artist, Intimidate, and Ride), the Concentration skill, or any abilities that require patience or concentration, nor can he cast spells or activate magic items that require a command word, a spell trigger (such as a wand), or spell completion (such as a scroll) to function.

Concentration

To manifest a power, you must concentrate

While raging, the Goliath Barbarian with Mountain Rage becomes Large size, always. That's different from increasing to the next size category, and any prior use of Expansion is overridden. When the Psychic Warrior/Barbarian is raging they are prevented from manifesting any power, so Expansion is impossible after they use Mountain Rage.

No stacking of these two effects is possible.


Edit: @Aegis013: There is no Q 1598 yet.