I have not come across a preamp with 2 ADJUSTABLE OUTPUTS. Cajunpepe mentions the Macs - do they really have INDEPENDENTLY ADJUSTABLE outputs? if so, then you're in luck :-)
MY Sonic Frontiers SFL-2 has 4 outputs: 2xXLRs + 2xRCAs but they cannot be individually adjusted; i only use the XLRs at the moment but for a time did a bi-amp using 2 identical Musical Fidelity XA-200s via the 2 RCA outs. i have not used different amps or same amps but different power outputs, otherwise, i'd use a good x-over for that.
.e.
MY Sonic Frontiers SFL-2 has 4 outputs: 2xXLRs + 2xRCAs but they cannot be individually adjusted; i only use the XLRs at the moment but for a time did a bi-amp using 2 identical Musical Fidelity XA-200s via the 2 RCA outs. i have not used different amps or same amps but different power outputs, otherwise, i'd use a good x-over for that.
.e.