What to do with broken McIntosh Pre-Amp

No it makes No sence a fixed Mcintosh preamp is much better quality then any piece of junk for $750 please remember when you buy anything new roughly 25% or less actually goes into the item the rest a R&D overhead and markup.
that piece you have would sell for $3-4K  new it may cost $5-600 to fix 
send it in and get a written estimate .  In the mean time with Khorns 
you can run any thing on them while you are waiting they are very efficient.
I was at a demonstration where a Paul Klipsch hooked up a 9 v pocket radio 
up to a K horn around 1980 and was very loud  at maybe 1 watt.grest Classic a Loudspeaker.

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.

Well, it is an older model not actually known for being that great.  Get a repair estimate and then make a decision would be my advice.  You might be able to purchase a new item that is much improved for close to the price of repair.  You may also wish to use a different brand, but that is up to your personal room and ears.

Cheers!

Everyone knows "someone special" to fix your McIntosh MX 114. So? I do, too. He has a video series which runs to the hundreds of videos... and can fix ANYTHING. His name is Paul Carlson, of Mr. Carlson's Lab on YouTube. He will do WHATEVER needs to be done and owns more test equipment than some laboratories, much of which he has buffed. Listen to him, he knows all, but his usual money stream is fixing switching mode power supplies for CNC machines. His contact info is on his site. From the US (as he is in British Columbia), call 206 259-9312 from 8:30 am to 4:30 pm AT HIS LOCATION in Canada. 

If you choose not to get it fixed.  This is an alternative.
https://www.schiit.com/products/saga-2?gclid=Cj0KCQjwz8bsBRC6ARIsAEyNnvqllaIsuLvQd6vC9HJQ7IwdvF_3v0WJXXWKUVx4PNYqMhNHcDVJS-oaAm6HEALw_wcB