I have received my EF2A amplifier today still waiting for my DAC to arrive; how should I connect the amplifier to my computer in the meantime? what input is the best? I can either connect it with an USB cable or an RCA to 3.5mm jack at the back of my computer. So far I've noticed that the...

So, I was wondering whether or not there is a noticeable difference between lets say an Audiquest Sydney cable and an Evergreen one? Also wanted to ask people who have the EF2A amp for any tube suggestions, the current stock ones produce a silent distant buzzing (?).