I would think people pick PB5 to complement D16, rather than choosing one instead of the other
I mean, PB5 is just an analog dual nutube amplifier, it needs an analog source to "amplify" the input. D16 is DAC/amp, you just need to feed it with a digital source, like your phone or another DAP, and it will do its D/A magic with its own internal amplification which gives you a ton of power. Now, relative to IEMs, where PB5 comes into the picture is to enhance/color the output of D16. PB5 has a warmer analog textured tonality with a huge soundstage expansion, and you can use it directly from D16 LineOut or even double-amp it from D16. I covered a lot of it in my
review.
Since we are in iBasso thread and relative to iBasso products
, if you want a simple solution for your smartphone, DC Elite will be all you need to use with IEMs to give you hi-end sound. If you don't want to drain your phone's battery, need higher output power, want more input/output flexibility with enhanced functionality, and enhanced analog tonality - you step up to D16. Then, if you want to add more coloring to your IEMs, you add PB5 to your audio chain, D16/PB5 have a great pair up synergy. If you are using full size more demanding headphones which require a more powerful source to enhance their audio performance (not just the tonality), adding PB5 to your source will be important as well.
The route of Smartphone/D16/PB5 vs DAP/D16/PB5 (btw, I was pleased with DX260/D16/PB5) will be up to your preference. I recently had a discussion with a few people who couldn't take using their smartphone as a digital source because of non-stop notifications which drive them crazy and interrupt music listening. So they prefer a dedicated DAP source. And then, there are others who enjoy their smartphone as a source, especially on the go for streaming where they don't have access to wifi. As they say, YMMV