I am looking for ideas for a DIY amp/pre-amp or integrated.

Got a good laugh out of this. Thanks for advice. I actually did consider getting an old Kenwood KA-3500 (just like what I bought brand new in the late 70s or early 80s). Couldn't believe the prices on eBay and elsewhere. I built a couple of full range single driver speakers using Mark Audio 10p drivers and am pretty happy, but I have a tube amp that only puts out about 3 watts and the speakers are just on the edge of efficient enough. I will check out the ESP P3A. I also found a Class A on diyprojects.com that puts out 30 watts and is really simple.
OMG: another person who had a Kenwood KA-3500. I wish I had kept mine so that I could sell it for the apparently outrageous amounts I've been hearing about on DIYAudio, as it was in perfect condition when I retired it and took it apart for recycling. It was good for its day as a SS amp. But heavens, I would not purchase that as "vintage" today. That would be madness.
 
As you come towards this stage of life sometimes you want something that simply works and works well with no drama and you want it really good because it is possibly the last one you will build and will now know how to do it well.
If you are in this frame of mind, you should seriously consider what Neurochrome audio offers.
https://neurochrome.com/I have built the modulus-86 and also used the Universal buffer. Seems pricey initially but the end results will totally dispel that. Remember the key thing is that the results are going to be as published and the same cannot be said for many DIY projects.