Is there something wrong with the sound that you're getting now that's leading you to try all the different DACs?
Seems like you've settled that there aren't differences in your system, so maybe the best route would be to keep buying cheaper and cheaper DACs until you find one that finally sounds worse. Then keep the model right before that one, sell the others, and recoup your money.
Or, if you really want to know what's possible in your system, just go ahead and get a new MSB Select. If you can't hear that as different, then you can put the question to rest once and for all.
Seems like you've settled that there aren't differences in your system, so maybe the best route would be to keep buying cheaper and cheaper DACs until you find one that finally sounds worse. Then keep the model right before that one, sell the others, and recoup your money.
Or, if you really want to know what's possible in your system, just go ahead and get a new MSB Select. If you can't hear that as different, then you can put the question to rest once and for all.