basically you need speakers that are higher rated than each channel of your stereo and you'll be fine... your stereo sticking out more power than the speakers can handle is obviously going to blow em like you did
not had any problems so far with a set rated for about 100w at the back and 75w up front - and they're plenty loud enough to really rattle the shelf at 85% volume and seem too damn loud bouncing off the screen (with the fader set a good way "back") - my HU sticks out 4x45w...
apparently theres a risk of blowing the amp fuses if the speakers are rated vastly too high (more than my 2.2x, i hope! been no sign of it so far...), but should be little risk of that with 60w vs 40w...
question is - what ratings system does your head unit use? There's RMS, PMP, PMPO etc etc... each of which gives quite different watt ratings to the other. If both speakers and HU are RMS then you're golden, go for it (and if its another set of JBLs you should be quite happy with the sound quality... i am with a pair of 3"/8cm ones of theirs! just needs a *little* help from a set of woofers to properly fill it out, walkman sized speakers cant be expected to have stunning bass...)
as for the return, you might get lucky - they might start asking questions if you're going back for a second go though! (such as.... ok, you have a 10w factory stereo, you've bothered to put good quality speakers on it for some reason... and now you expect us to believe our precision manufactured items have blown whilst connected to it... pull the other one
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best of luck mate
(i mean, its not like they warn you of such stuff at the shop! i could have put these JBLs onto a 150w per channel monster, full-forward fader with no warning and totally destroyed them without realising... did the guy on the desk ask me what power my stereo was, did he heck
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