What a saga!!!! I have to agree it really sounds like a defective machine - and your lack of trust in the local "repair" center seems to be "well earned". (Yegads - how do they stay in business???) I have been careful to save all these posts, as my better half has still been too involved with other things to be able to get her machine up & running - I do NOT relish the thought of having to go through even 1/10 of what you've been through to get things playing. I'm guilty of assuming that things "featured" should "play well together".... Guess I'll learn soon enough, though. I'm seriously considering investing in a "diagnostic tool", that being one XL-5000 card WITH something on it. I have hopes that will help determine if any issues are compatibility or hardware related. I think I speak for all who have followed your saga in wishing you a speedy solution!!!
Best Regards, NGA