Cheap Chinese AK4490 boards

I have an AK4490 DAC board which I'm quite pleased with. I'm thinking of getting a second board where I can adjust the gain on the op-amp output. I've seen this one with leaded components which would make the task easier, however there is no information about what kind of USB input board is needed or how to connect it. I'm not too confident about getting such information out of the seller, and it would help if anyone here could advise me.

Upgraded Assembled AK4490 Chip EQ II2S DAC Decoder Board 32BIT 768K

Upgraded Assembled AK4490 Chip EQ II2S DAC Decoder Board 32BIT 768K | eBay
 

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Right now I have an extra gain stage after the DAC using a LM4562 op-amp. I was thinking about the possibility of increasing the gain of the op-amp on the DAC so an extra stage would not be needed. The extra LM4562 stage is needed because I have a 2 stage tube amp which needs a bit more gain.