Do I need a streamer?

It really depends what you are after. Good sound that you enjoy or great sound… the best you can achieve with your budget. So, it gets complicated… what is your budget… <$10K? Then it is going to matter on your components. But once you break a certain level ($ being a proxy for quality)… then the PC / MAC becomes a anchor holding your system back.

In budget systems, MACs and PCs as streamers are reasonable choices. But at some point one has to move up and get a purpose built streamer to replace a computer. It is easy to rationalize the level to be far above where you are… but this can frequently be rationalization. In general, an equivalent valued streamer… say $1,200 will sound better than an equivalently valued PC… given appropriate audio components.

@whitestix 

Fibbr is nice brand in fibre optical cable. 

if not getting streamer, you can upgrade a RECLOCK to enhance the signal quality from your Mac. check this little reclecker with psu boost : iFi SPDIF iPurifier2. this is also an option of enhancing the sound quality instead of replace by 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