f it was my money, I'd recommend you upgrade to an outboard DAC, I do not see the sound improving much doing another streamer. A quality DAC is going to have the largest increase in sound considering your options. A streamer’s internal DAC is generally not that great overall. And the streamer itself is a minor improvement if at all within a reasonable budget.
The Blue OS is actually quite good as far as streamer OS’s go. Better than the Aurender conductor app by far from my experience. I’ve had a few streamers now and after my time with an overpriced Aurender I ended up back to the Blue-sound streamer (Vault2i), I have an excellent DAC so it’s not that noticeable. And if I'm honest the OS/App for the streamer to me is the number one thing to consider when buying a streamer.
Try an outboard quality DAC and see how things sound. I’m betting that’s your sweet spot in your choices.