HPA-9 is the best headphone amp in the world, feel free to compare it against anything at any price.
But it can also be used as a class A preamp. If you have very good analog source, and want to bypass the A2D of DAC-9, then follow this setup where the HPA-9 RCA outputs go to STA-9 RCA inputs.
And the DAC-9 balanced outputs go to STA-9 balanced inputs.
It is a little inconvenient to use the balance/unbal switch of the STA-9 but if you want the ultimate purest phono to amp solution and still combine your best digital source, this is the only way, and may be only one in the world that can do it.