I’ve a set of 2.1 (two speakers + sub) that I’ve had forever. Someone told me I have “the unicorn” of computer speakers. Its a Monsoon MH500 with planar flat panel speakers and powered sub. And its been working well since I got the set in the year 2000! I paid $60 for the set, and now, find the only issue is the remote-corded volume is oxidizing inside and creates static as you raise/lower the volume (worn potentiometer I would guess).
I think if I had to replace this when the external power brick fails (common death of this wonderful sounding setup), I might look for another power supply, since crossovers don’t fail, nor speakers unless over driven. The controller in yours likely has some component failing and as you, not an EE to open up and start running 'scope on components without schematic or previous repair expertise with the Altec.
That said, Klipsch has a 2.1 THX setup, as well as Logitech has some inexpensive but nice sounding products Z533 and Z333.
Now, this is just a fantasy suggestion, but there are some folks with healthy ears, great musical taste and “price is no option” wallets that Cambridge Audio has some speakers, a subwoofer, and separate amplifier w/DAC that would still be less than a fully loaded new iMac yet sound amazing!