Seems that since people would have to replace components when digital tech exceeds capabilities of legacy equipment (ie S1 v S2), a Modular approach might be better to upgrade your system products.  Separate the digital processing aspects from the audio/analog-power systems and provide modular pieces.  Provide a way to plug and play upgrades.  This way you may be able to update processing without people having brick components or separate between controller system versions and pay for replacing a perfectly good audio portion.  You might also be able to release audio system module upgrades as well.  Of course, this may not be your current business model, but some good System Engineering could help you solve these business issue problems.