What should I upgrade?


I am in a generally noisy environment, so I tend to stick to headphones, I'm currently setup with my ASUS Xonar Essence STX PCIe Card (TI Burr-Brown PCM1792A DAC 24/192 W/Stock Op-Amps), a pair of Sennheiser HD280 Pro headphones (I think might be the weak part here, they're old as well)

My non headphone setup is the ASUS Xonar card, a pair of Polk TSi 100 Bookshelf speakers, Yamaha RX-V365 Reciever for analog amplification, also of note is that I have primary audio reflection points insulated with foam.

I'm on a budget but willing to save, what component would I need to upgrade, or add, to get the most bang for my hard earned buck? My target audio file is 24/192 FLAC/WAV when I can find them.
zunaro
ditch the Xonar DS and buy an HRT Musicstreamer II. I've given one to both my college age sons as the best budget music purchase for PC audio. If you have enough cash left consider one of the Schitt headphone amps for headphone nirvana. I've played with the Xonar DS and the Essence STX...the first is a good gaming card but can't be seriously used for music. The Essence is musical but can't overcome jitter issues the way the Headstreamer II can.
The HRTs are very very good, a real value leader, but given your budget constraints, you might want to consider a DAC/headphone amp combo. If you like the Senn sound, the 580s are considered very nearly as good as the 600 or 650 and much cheaper.
I found AKG K701 step over the performance level of Senn650.
They're the only ones I could listen for long long time.
But those AKG 701s need some power.

I would look into upgrading your headphones and getting a headphone amp. There is a $99 Schiit amp that might work well with headphones that aren't too demanding (maybe check at Head-fi to see how the 701s pair with the $99 Schiit).
AKG 701s are very good, for sure. My thinking is that OP is on a budget, likes the Senn sound. The 580s (and 590s I think) are considered very very close to the 600s and are much less expensive. That might enable the OP to get a headphone amp, as well, which I think would also be very important for upgrading his system.