Agree with Firevortex.
I did it with a pair of needle-nose pliers (to get the nut off the front of the volume control; Firevortex, shame on you, forgetting that extra 30 seconds!
) and a screwdriver.
I'm two left thumbs, and was able to do it easily. My 2.5 is brand new, but I listened to it for a couple hours last night with the stock amp and discrete amp. Discrete, to my ears, has tighter deeper bass, slightly better resolution/clarity in the mids, and a more extended top end. Better image placement of instruments and voice with the soundstage. Worth the extra $ to my ears.
I even compared the amp to a Lunch Box amp I'm using. The Lunch Box is KILLER at < $200, and it did clearly show up the Zhaolu discrete amp (more "organic" sounding, a little bigger soundstage). But it told me that, while the Lunch Box can compete with amps 2-3 times the price (I HATE that phrase, but I truly believe it here), the Zhaolu is likely competitive for more than it's price, too.
For those looking for good sound and convenience of the all-in-one, the discrete amp is a very worthy starting point IMO.