I am an Opus owner and have been since its release (including the upgrades). I too love this player... sounds great and is a very versitile unit. I have used RCA, balanced and DIN outputs in various configurations. I agree with the owners and reviewers concerning the DIN output being the clearest and best path to the music. I DID NOT however notice a difference between the RCA and balanced outputs in terms of quality of the sound (I mostly have used the balance outs directly to a Krell FPB 300c amp).
About a year ago I inserted a preamp (AES AE-3 DJH Signature from Upscale Audio) and would recommend that you add a preamp instead of changing out the amp. I don't think you would gain as much by simply going from RCA's to balanced outputs. A good preamp allows you to use the DIN output and gives depth to the music and more weight to the bottom end. Without the preamp the Opus 21 had a great soundstage width but lacked depth in that soundstage. Just my experience and two cents.
About a year ago I inserted a preamp (AES AE-3 DJH Signature from Upscale Audio) and would recommend that you add a preamp instead of changing out the amp. I don't think you would gain as much by simply going from RCA's to balanced outputs. A good preamp allows you to use the DIN output and gives depth to the music and more weight to the bottom end. Without the preamp the Opus 21 had a great soundstage width but lacked depth in that soundstage. Just my experience and two cents.