We are not really answering your question, what decently priced preamp would be a good choice? I don't know.
That is to keep the McIntosh amp and Klipsch Speakers. Putting aside sentimentality (I still use the equipment I inherited from my wealthy uncle) I would first question that decision.
If not an audiophile, or, even if you were, who says that is the equipment you would choose, which means, keep it for sentimental reasons, or move it along.
Klipsch Cornerhorns? What model? They are quite large and might not fit your listening space. Because they are highly efficient, the amp will not need to do much, so the idea of a 'switcher' then direct to the amp could work, but, consider volume.
I use a Chase Remote Line Controller, love it, it has remote volume, input switching, and, a feature I truly like, remote balance. A small tweak to the balance of some tracks makes a large difference I found.
here is new in box, $50.
https://www.ebay.com/itm/wireless-adapter-Remote-Line-Controller-New-NIB-CHASE-RLC-1E/372651830886?hash=item56c3c7ae66:g:lDAAAOSwnXhcspCn
Then, get familiar with the amp and speakers, (they might need some work too), and decide, fix the pre-amp, keep for future options, sell as is.