#1 M-Audio Fast Track (mk1) gain and 18650 Li-Ion mod / upgrade

So i had this old, pre-"facelift" M-Audio Fast Track since 5-6 years ago, which had been lent to a bandmate for the last couple of years. A few weeks ago, i traded him up to a Scarlett 2i2, and i got my Fast Track back.

And then i got thinking - it has the convenient mono/stereo switch on the front (to have both inputs in mono, or input 1 on the left and 2 on the right), a headphone output, doesn't need a specific power supply (it being bus-powered)... 😏