Burson Opamp V6 Vivid Dual x 2, Burson Opamp V6 Classic Single x 2, are using on an unknown brand China-made DIY Dual PCM1794 DAC, they are replacing op amp muse01*2 and opa637sm/883B(UK)*2. The bass response is enormous but not bulky; the mid-high range for string orchestra is smooth without a second of edgy sound; mid-frequency range for the vocal response just as good as Neumann U87 on vocal, with an integrity of the vocal timbre, mid on piano music is also very good; the overall dynamic is tamed but powerful enough, the soundstage is properly wide and depth to provide a focus of central audio image from the sound source. Last night, all 4 opamps (all PLUGGED with the original 8-pin Op Amp Adapter Stand) ran for 6 hours. Tonight, all 4 op-amps (all WITHOUT PLUGGED with the original 8-pin Op Amp Adapter Stand) ran for another 6 hours. ***I have found that the V6 op-amps, directly plugged onto the PCB without the adapter stand, perform a much denser of sound and more smoothly on different frequency ranges. In other words, if the adapter is not necessary, unplug them for a more good sound!***