+1 on Georgehifi counsel.
Perhaps rather than a traditional separate preamp, consider an alternate solution. I do not like my OPPO 105 direct to amps for audio. Besides it doesn't have analog input. SO, I use a bel canto design DAC3.7.(which is a DAC/PREAMP w external PSU, analog input, balance and volume control and full function remote) My phono preamp is plugged into the bel canto 3.7's analog input and OPPO in to it via coax. Extremely satisfying in all ways audiophile and most of all sounds and feels like real people playing music on real instruments in real spaces. Every preamp (active and passive) introduced (up to $12k) detracted from the fidelity. Hearing your listing musical first and my experience with OPPOs leads me to wonder if the OPPO with it's Sabre dacs and output stage might not be your ideal musical sound. Don't think you'll that dac and output stage sound signature to your liking by inserting a conventional preamp into the signal chain - regardless of brand or tweak. My sense you will be happier with a more musical DAC/PRE than with a conventional preamp. And later when you can a better transport. Best wishes.
Perhaps rather than a traditional separate preamp, consider an alternate solution. I do not like my OPPO 105 direct to amps for audio. Besides it doesn't have analog input. SO, I use a bel canto design DAC3.7.(which is a DAC/PREAMP w external PSU, analog input, balance and volume control and full function remote) My phono preamp is plugged into the bel canto 3.7's analog input and OPPO in to it via coax. Extremely satisfying in all ways audiophile and most of all sounds and feels like real people playing music on real instruments in real spaces. Every preamp (active and passive) introduced (up to $12k) detracted from the fidelity. Hearing your listing musical first and my experience with OPPOs leads me to wonder if the OPPO with it's Sabre dacs and output stage might not be your ideal musical sound. Don't think you'll that dac and output stage sound signature to your liking by inserting a conventional preamp into the signal chain - regardless of brand or tweak. My sense you will be happier with a more musical DAC/PRE than with a conventional preamp. And later when you can a better transport. Best wishes.