I need some amplifier help

I have an Adcom 555 and an Adcom 555II. Right now I am using them to power a pair of B & W DM640. I am using the 555 for the left ch and the 555II for the right ch. Should I keep it this way or change it to one amp for the low end and one amp for the high end? Just wondering because of the fact that the 2 amps are not exactly the same. Also, am I losing a lot of signal splitting the lefts and rights coming out of the preamp and is there any other way of doing it? I split the left to both ch of one amp and the same with the rights. Any suggestions will be appreciated.