Why a transport over a CD player?

You already have a good DAC. I would get a transport, but only a good one. All in one players generally do not have jitter reduction, since they don't need it. However, when you separate transport & DAC, jitter becomes a problem. That is why the better transports incorporate "reclocking" circuitry near the output jacks. This has a great effect on sonics. But reclocking or reducing jitter is only one facet. And you won't get this when you use a player as a transport.

In your price range, Sonic Frontiers SFT-1 is a great transport and matches well with Theta. Theta's older Basic II transport is also good, though not in the same league as the Sonic Frontiers. Theta's newer Jade may be equal or better than the SFT-1, but is more money.

In your situation I would prefere to get a good quality dedicated CD transport. Having a good quality DAC means that you will hear all digital "dirt" that is comming out of the bad CD-transport/player. The integrated designs just seem not to have a jitter. Once you'll plug CD player into separate DAC you will find out the truth whether CD player has or hasn't the jitter. Also many people will say that they tried to connect different DACs onto their CD players and realized that CD player sounded better. That's often happen with low quality CD players that have poorly designed transport.
There are plenty of good used under 1k CD-transports that with your DAC will outperform today's $2500 integrated CD players! Check out Theta Data II, EAD T-1000...

I endorse Kevziek's advice. You can find used Theta Data Basic Is and IIs here for between $400-600. I have a Theta Pearl which I'm using with a Bel Canto DAC1.1. I came very close to getting the Sonic Frontiers SFT-1 but it's at or above $1000. The Pearl cost me $600.

Your Theta DS Pro Basic II is a good DAC. Keep it and save a few hundred bucks buy getting a Theta transport. Although the SFT-1 is pretty cool looking with the gold and silver faceplate. :•)

Good luck and happy hunting!