What those guys said you need to use the power brick. From what I read there is no reason to upgrade the power supply it puts out enough power for this amp. I had one that was 2amps more so I used it.
From what I found those Op Amps are $70us. An op amp is going to make close to zero difference. And from what I read if anything those op amps have a forward/bright sound which this amp already has.
The VX1 has not been a popular model and the DIY crowd would consider it vastly over priced so you are not going to see many people modding them.
An amp based on the TPA3116 chip will sound very good out of the box but it is just an amp, not a DAC.
This is the one that the really smart amp people tell me has all the right bits already installed. Very musical sounding Loudness wise it about equal with the VX1, but as it goes louder it stays cleaner than the VX1.
This is the model to get, as I said it already has all the electronic bits installed. But its nothing fancy, an on off switch and volume.
http://www.aliexpress.com/item/Free-shipping-original-SMSL-SA-36A-2-20W-High-grade-HIFI-Digital-Power-Amplifier-Class-T/1701910957.html - to get a line out for a sub. And I wanted something in a box.