Of course you can also get rid of your KI256 by fitting a Garmin G500 or Aspen EFD1000 EFIS with the appropriate autopilot interface unit and then for the mandatory back-up you can have a standard vacuum horizon from RC Allen, SigmaTek etc.
Incidentally, I have an S-TEC 30 in a PA28 and it's been pretty flawless for 7 years. We do install STec systems at work and know of the shortcomings but as with all things at the cheaper end of the Market, you get what you pay for. Once an installation is completed properly they tend to be pretty good. STec rate-based systems tend to have poor performance in higher speed aircraft but for the top end of their Market, STec make the 2100 Intellipilot which is attitude based and this does seems to work extremely well. Unfortunately the 2100 is only STCd on a limited number of types - typically twin turboprops such as Cessna 425, Twin Commander and KingAir.