I have a DAC with pre-amp functionality, the SMSL M200. In DAC mode it outputs the typical 2V via RCA and 4.1V via XLR, but in pre-mode it outputs up to around 2.7V via RCA and 5.5 vs XLR. Now the input sensitivity of most amps I've looked at are much lower than 5.5 V, but many still have XLR...