I use an Aune X8 with a Sparkos opamp and found it slightly outperforms my D70s on RCA outputs on fixed outs in my system. Geshelli also allows this upgrade I believe. Can add an Aune linear PS and will cost under $500 retail, less if all bought on sale.
Using the Aune as a pre works but not as well as the fixed outs IMO but it has that option if needed utilizing both RCA and XLR outputs but I don't expect it to be fully balanced in XLR. Cheap but more than expected performance on fixed/full output.