Sorry to hear of your troubles with the ARX; it is another in a long line of Walther/Umarex-made .22 clones with something of a mixed reputation. I was intrigued by the gun myself, as it offers a lot of features, and I've seen it for under $400 at several online retailers in the past year.
I've handled a couple examples, and found the light weight and awkward forend ergonomics a bit off-putting. I too thought it might be a interesting Sig 522 alternative, but I've come to realize there is really only one way to match the Sig, and that is to buy one

:bthumb: My buddy's 522 has been nothing short of stellar in terms of performance and reliability - he's had it almost six years now, and I don't think it has ever malfunctioned for any reason. I've shot another friend's M&P 15-22, and though it isn't a bad gun (and takes most AR goodies), I don't think it's as durable, reliable, or well made as the Sig - neither is it much, if any cheaper, most of the time.
I'm not a big fan of the stiff-loading Black Dog magazines Sig uses (though they are highly dirt/grime resistant and very reliable), and remain disappointed that Sig has yet to fit a good set of iron sights to the design. Otherwise, it is excellent in every way - ergonomics, smooth trigger, ease of cleaning, etc. - and is easily the finest .22 LR semi-auto I've fired, and the most impressive rimfire rifle design I've come across :bthumb: :Blasting_
Kind Regards,
~ SH ~