regarding stepped attenuators, they are available for the marchand, but phil marchand said not to bother, i wouldn't be able to hear any difference. he says he has to offer them because some folks aren't interested in his product, otherwise. i also asked him about balanced vs single-ended. he said that if you get the xm-9 balanced, it is a true balanced design, different from the single-ended unit, not just w/different connectors. he then went on to say that it is only worthwhile if you have a noise problem, otherwise it offers no sonic improvements. of course, if your amp & pre are configured in balanced-only mode, then it also makes sense to go this way.
re: plug-in x-over frequency modules, i much prefer the simplicity & lower cost of doing it this way, as opposed to having a switch. it only takes maybe 3 minutes, & i do it *so* infrequently, that it's not really an issue.
i also much prefer having a volume pot at the cross-over frequency - this really makes it easy to match different subs w/different speakers, in different rooms. w/my present set-up, the increased clarity, detail & smoothed frequency response (confirmed w/a pink noise generator & spectrum analyzer) when the x-over volume pot is set to -2db, is really noticeable.
regarding use of i/c's vs op-amps, in this day & age, i think it's more of an intellectual argument, w/no real-world meaning - plenty of outstanding audio products w/op-amps. they *can* offer sonic benefits to a savvy designer...
don't get me wrong, i'm sure the bryston is an outstanding unit. it was one of my 3 choices (the other being a db systems unit). it just didn't make sense to me to spend the extra money when there didn't seem to be any significant sonic improvements to be had, & when it was actually less flexible for my purposes, w/o the x-over volume pot. i *can* honestly say, tho, that i wouldn't trade my unit straight-across for a bryston, fwiw... ;~)
regards, doug s.