That's upgrade priority; purchase priority doesn't work like that, meaning that's only when you have all three. If you don't have one of the three, priority is to get that missing part first. You wouldn't be able to connect your computer via usb to the Lyr... You'd need to get a 1/8" to RCA. Still, you'd get garbage.
Not if he's using iPhone or computer motherboard.
Get an amp, AND a DAC. Within your budget. Magni/Modi. O2/ODAC. Bifrost/Lyr if you can spend a bit more.
That depends on if you're planning on upgrading later on. Magni/Modi and O2/ODAC are very easy to resell and offer one of the best price to performance ratios, and will also suffice with the LCD2. I mean you can get a Magni and Lyr, atleast that's something. USB is digital, and RCA is analog, meaning no bueno.
Stay clear of the Valhalla for the LCD2's its tube only and doesn't give them the current they need. It's designed for high impedance cans like 650's T1's etc
If you see the previous post, the magni isn't sufficient, said by the schiit staff themselves.
Plenty of people have used the LCD-2 with the M&M stack with no problems.
With that said, the budget Schiit isn't bringing out the LCD's to their full potential.
But the stack is solid and easily listenable.