IMO...
your Sony STR-DA2000ES, when fed a digital PCM signal from any source..and being in direct 2 channel mode, is an AMAZING SOUNDING amp. You'd have to spend upwards of $5k in sperate componants to top that soundstage, detail and imaging prowess.
That said...
the ONLY way to listen to one of these amps is by feeding it a digital signal and taking advantage of the Sony S-Master pro wizardry (which upsamples incoming PCM to DSD..hence the magic).
so, its the tranpsort that will make a big difference. Any new or old higher end Sony DVD / CD player should perform wonderfully as they are supposed to be exceptional tranpsorts on their own, from what I understand. I think big, heavy and well built players make for nice tranpsorts vs. the thin and flimsy plastic consumer players that are available these days.
The thing w/CD players..its about the tranpsort and build quality (one and the same) but more importantly, its all about the DAC inside. The better the DAC, the better the sound. pure and simple. And IMO, the DAC in the Sony 2000, 3000, 5000 and 9000es recievers are better sounding than most other stand alone DACs out there that cost under $2k.
I think you're on the right track where you are.
as mentioned, trust your ears. Keep listening to different gear and come to the conclusion that you all ready have a great sounding system.
A lot of the cheap $200 and less CD players have nice DACs in them,...but are lousy transports.
Many of the $1000-2000 CD players are great transports w/mediocore DACs in them. When you get the best of both worlds together in one box, those are the good decks.
as per CD players and my own observation....
I went from a Musical Fidelity CD-PRE24 which is a GREAT sounding CD player....to a $58 best buy Toshiba 3960. I had the two units running head to head and could not hear a difference. My system at the time was certainly up to the challange of showing me points of reference between componants.
Now, I run that same toshiba into a 3000es Sony amp. 1/4th the cost of my individual componant rig. 10x better sound.
still, I could stand a better transport to improve things a little bit.
I think an approach to try would be to better the digital signal. Something like the Apogee Big Ben master clock would do VERY nice between any transport and DAC.