The 25 amp is class A..not A/B even at higher volumes.
from stereophile.com
"The XA25 stereo amplifier is the latest addition to Pass Laboratories' XA series of amplifiers and, at $4900, the lowest priced. It weighs only 45 lbs, has single-ended inputs only, and outputs 25Wpc into 8 ohms, 50Wpc into 4 ohms, or 100Wpc (!) into 2 ohms. According the XA25's well-written owner's manual, it will deliver 50W peaks into 2, 4, or 8 ohms—in class-A. "