The LA90 doesn't have RCA. Only XLR and 1/4" TRS Bal.
There's no need for such an expensive DAC. The SMSL D-6 or DO100 will give you the same 100% transparent sound and Balanced output as the D90, for a fraction of the price.
Sorry I meant I was using RCA from my Heritage DAC into unbalanced TRS... More so if there is a significant gain advantage from unbalanced vs balanced XLR...