Which Oppo 205 digital output you plan to use? SPDIF or HDMI?
Please note that Oppo 205 SPDIF output is 'scaled' to 48k when playing Blu-Ray or SACD high-res audio, and that's only for 2 channel. Also, there's no DSD output through SPDIF. PCM is limited to 192k when playing from USB media.
IMHO, you need more than your budget to have an external DAC better than Oppo 205 built-in DAC, and the external DAC must have HDMI input, something like Bryston BDA-3 (just an example, not recommendation).
Please note that Oppo 205 SPDIF output is 'scaled' to 48k when playing Blu-Ray or SACD high-res audio, and that's only for 2 channel. Also, there's no DSD output through SPDIF. PCM is limited to 192k when playing from USB media.
IMHO, you need more than your budget to have an external DAC better than Oppo 205 built-in DAC, and the external DAC must have HDMI input, something like Bryston BDA-3 (just an example, not recommendation).