I don't personal experience with both, but reviewers I trust really rate the Topping. I decided against upgrading to a topping Amp recently due to the high price in NZ, and the fact there have been reports of reliability issues with the Topping Amps, reported by a number of sources, and with the delays in shipping from China and the likely headaches with support, I'll make do with what I have. I suspect a batch issue or something with the topping Amp, and I can't speak to the reliability of the Dac/Amp Combo.
Sorry, not sure that makes it clearer. Right now, I'd buy the Topping if I could find it at a decent price in NZ where I was protected by a local warranty, because I think it's a truly exceptional device.
Neither seem to support MQA, not sure if that's something you'll miss. Pretty mixed reviews for MQA, some people say it's great, others can't tell anything different about it.
I'd struggle to justify 2.2x the price for the RME, I suspect it *might* be a couple of percent difference. YMMV