So in other words, the main cause of the problem doesn't lie with the technomancer, but with the fact that your group intentionally gimped themselves for style points. Cool characterization, but it does affect the balance of things.
Also, the techomancer is the only one who's totally familiar with the system and into optimizing characters. The others are under the impression that they've got decent stats. And I'm not sure they don't, for very specific circumstances like fighting a heavily armored opponent.
Now that you mention this, it strikes me that the technomancer might actually be trying to stay (relatively) low profile in combat and not just eat everyone else's spotlight. Or maybe he just likes battlefield control effects. Disabling an enemy is effective at that level of group optimization, keeps him alive and everyone else feels like they're contributing. If that's not the case you may have an issue though, but from what you're saying no one feels massively overshadowed.
Just make sure you don't back him into a corner (though from what you've said he should have plenty of background objects to turn on corpsec).
Against a single, heavily armored opponent, perhaps they do. Against anything else, however, not so much. This is the kind of group that could take out a main battle tank in the surprise round, but get wasted by a group of low level gangers who just got their first wires second-hand. The face is understandable, as there are other considerations there, but if the sniper and samurai are actively avoiding getting extra IPs, then they are the reason the technomancer looks so good.
What you may need is an object lesson in the power of additional Initiative passes. Wait until the next time they run against Renraku, and have a squad of Red Samurai on site. Whether that is in the intel or not is up to you, but I'd go with surprising them. Use the stats in the SR4A book, and have a four-man squad. Be nice, and put gel rounds in the assault rifles. The reason being that there are things in the area that react badly to bullets, in the "Oh god, we're all gonna die" kind of way. Any of the group that gets knocked out gets to play the "offer you can't refuse" game.
Or, if you want something more towards their level, but still showing an object lesson in the power of IPs, have a rigger work against them, with several drones in concert. Show them what a difference having just one extra IP means, especially when there is someone in the system keeping the TM from simply waltzing in to disarm the threat.
I say this from personal experience as a player. A TPK, now and then, can be a good learning experience, especially when you didn't know there was a lesson you needed to learn. Now, should every encounter be trying to wipe the players out? Of course not. But every once in a while, you have to throw a fastball in on their hands to keep them honest.