So your amp has a 1/4" out. Adapting that to an XLR is not going to do a damn thing, its still the same signal, in fact it may be worse because then you will be feeding a line level signal into a mic preamp. Of coarse you are probobly feeding a Mackie or something which you can trim the gain down for line level, but I think there is a better way.
I am also going to recomend a DI. Get yourself a DI and stick it in between bass and amp (after effects if you have them). If don't know how a DI works its simple. It takes your unbalanced Hi-Z (impedence) signal (from bass) and converts it to low impedence balanced (XLR) mic signal. It also passes your Hi-Z signal through so you can still run your amp. Now you take an XLR cable and run it from the DI to your mixer or whatever XLR input you are using. Now set your levels and record. The downside of this is that you will not be getting the sound of your amp, for most people with crap ass amps this is a good thing. If you are absolutely in love with the sound coming out of your cab, then buy a mic and mic it. Either way you will probobly be better than using the 1/4 inch out on your amp, those little add on's hardly ever sound great.
Of course always remember "Garbage in, garbage out".
Oh, and if everyone lived by "The right cable for the right job the world would sound a lot better".