Do I need a streamer?

I'd suggest what many have said, dump the computer and go with a dedicated streamer.

If not then you could use a DDC to reclock the data, then output to your DAC. I use a $500 Denafrips Iris DDC, but I'm using a Bluesound Node 130 and just streaming.....not attaching storage like you have. The Iris isolates the USB input both galvanically and optically, and reclocks it with a high quality TCXO crystal.

If you have an interest, check with Alvin Chee at Vinshine Audio.....he'll steer you in the right direction.

Yes you are.  A $300 streamer (IFI or Allo) will be a big upgrade to your computer.  After that, return on your $ is limited although I ended up spending the money for an Innous Zenith MK3 and love it.  

@whitestix

if one is streaming using a standard computer then a streamer is not needed per se, but one might well sound noticeably better -- but really no way to know without trying it yourself

here are three quite well respected, very good performing, cost effective streamers, you can buy them try them and if no improvement over your imac, just resell at no or minimal loss

of course there are ifi usb purifiers available used too, can try that as well

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It seems to me that the issue revolves around the ownership of the music. Streaming gives you access to an enormous library of music - almost everything ever recorded! Streaming enthusiasts are often not interested in owning physical media, since they can "dial up" anything they want to hear anytime. Why waste space storing CD boxes, record albums (silverfish eat the cardboard covers), or even external hard drives if you don't need them? But if your cell phone towers fall down, or the local nodes fail, or a hurricane knocks out the businesses you !get your music from - no tunes for you!  Some of us old guys think it's normal to own your own music. "That's how we did it when Brubeck and Basie were alive!"

I use a 10 year old laptop feeding a Sony DAC and get excellent sound (as good as a CD anyway) and I can record it if I want via an outboard digital recorder (hand held, usable for recording live music/environmental sounds. It can handle 96/24 for live music and is way better than 44/16). Most streaming is CD quality.  I don't use wireless. It's only half as fast as a wired connection. Being an old guy, I don't mind opening a CD box, putting on a record, or (now nearly always) loading up music on a hard drive into my music playing software. My computer lets me write/edit music/edit photos/use the internet and stream music at the same time. If you like what you have, enjoy the music! If  you live in a "tiny house" and have no room for storing physical media, If you'd rather travel light and live in a trailer - stream on! If you enjoy the latest in hi-fi gear, buy it and enjoy the experience. Happy Listening.