Best USB DAC for under $1000

The Peachtree is a great way to go.
If you can stretch it a little bit, you might check out the BMC PureDAC.
The good news is, 14 years ago there was a huge disparity in DA performance. Now the playing field is largely even, and a $1,000 unit is better than the earliest $10,000 unit :)

Ifi Audio iDSD Mini will be about $1K.

The new and beautiful looking Marantz HDac1 (?) is $800.

I am waiting for a review to come out on the Marantz HDac1

Used Yulong Sabre DA8. I just got one and it is very nice indeed. It easily surpassed my Dexa'd Eastern Electric minimax plus, and is real competition for my NAD M51. Plus- it has an analog input, a nice headphone amp, and volume control- in other words, it can make a decent preamp too.

Consider a used Audiophilleo (if it has the PurePower, the better), with a Metrum Octave Mk.I. I have this setup which I bought new, and recently bought an exaSound e22 that retails for $3.5k and is new (and getting much praise). If playing PCM through JRiver the Metrum+AP sounds better. Much better. So much so I will be selling the e22.

FWIW, Steve Nugent from Empirical Audio has been quite vocal here saying the clock is where you should spend most of you budget.more so than on the DAC itself. That is what the AP with PP strives for, and the Metrum is one sweet DAC.