No, 2x6, slew rate has nothing to do with an amp's ability to control bass output. It's a measure of the ability of the amp to respond to rapid changes at the opposite end of the audio spectrum, e.g. 20KHz. If slew rate is inadequate the amp won't be capable of reproducing the highest frequencies flat and with low distortion. If these frequencies are reproduced well, as even low priced equipment of competent design does these days, then the slew rate has been shown to be adequate.
An extremely low damping factor in the low single digits(e.g. some tube amps having an output impedance of several ohms, rather than the 0.1 ohm typical of solid state amps)would have some effect on bass, but see the explanation of this point by speaker designer Dick Pierce which Gene DellaSala
published in Audioholics. Any competently designed modern solid state amp has a damping factor which is far more than sufficient.
