Buy a $40,000 used DAC for $4,000 or a new one for the same amount?

The biggest issue with old DAC's is how they handle Redbook.

New DAC's are sooooo much better high resolution files hardly are necessary.  Older DACs need the high rez files to sound their best.

So, 10 years is on the border of the DAC revolution. I wouldn't go there.

I’m sorry, but 40k on a dac? That’s a down payment on a house 🙄. How much better can it possibly sound as opposed to a 1k dac made by a reputable manufacturer. To each his own I guess...if I had 40 k I’d spend it on speakers, but I don’t, and if I did there would surely be a divorce lol...edit, now that I read it more carefully...4k for a once 40k dac...still way too much, only my opinion. I spent like 500 on a dac and to my ears it sounds fine, but what do I know...I’m mostly an analog first  guy .. now 4k on a turntable, now we are talking 😁

“New DAC's are sooooo much better high resolution files hardly are necessary”

erik,  I beg to differ here. Either you haven’t heard a high resolution file or you simply find 16bit/44.1kHz files more than adequate. 

Depending on the original source master, the high resolution files 24bit/192kHz and above sounds better than their 16bit/44.1kHz counterparts. Not that 44.1kHz files sound bad, the high resolution files simply uncovers more subtle nuances, warmth, depth of field and air around instruments and musicians. Of course, all of these ‘audible’ subtleties are very much system dependent. 

I have 25 year old Wison Grans Slam Series 1 that I was offered 4k for (original cost over 50K). One twitter was shot and the smaller woofers had to be reconed. I decided to refurbish the speakers and the total cost was about $1500. The speakers sound like new and I have not heard better (though I am sure better speakers are out there). 
I wonder what 40K speakers he is referring to.

I see all of your posts are asking the same thing.  Just because a product retailed for $40K does not mean anything.  I have read where people say something is built like a tank.  All this means nothing until you understand design and what makes something sound good.  A heavy chassis does not mean built like a tank.

It comes down to the design and parts used.

the high resolution files simply uncovers more subtle nuances, warmth, depth of field and air around instruments and musicians.

This statement is simply not true at all.  Most high rez files do not have warmth compared to properly designed NOS DAC designs.  They may have more detail but in my experience give up the musical sound quality that NOS has.  But having a DHT DAC, I don't give up anything.

Happy Listening.