Sounds like you need a Receiver with built in DAC (Digital to Analog converter)
but looking at your desk and setup that wouldn't look great.
What is your budget?
What speakers are you planning to use? Desktop speakers? separates? stereo speakers for music or do you want a subwoofer and rear surround speakers for blu-rays and games?
Edit: Just noticed you have PS4. I assume it has the same Optical Audio Out
For PS audio out, there are several options available. PS has Optical Audio Out as this provides the most direct audio path to a set of speakers/amplifier. I guess currently you are using HDMI and which is also fine. If your TV has an Audio Out on it, it is like a passthrough port so gives you more options if the speakers you find only allow single phono input or phono to 3.5 mini jack for example.
So, if you go for an AV Receiver for the most flexibility, high quality etc, keep in mind they are quite big and bulky but there are slimmer versions around. Basically you run everything into the receiver (both audio and video) and have one cable coming out of it to the TV, the receiver manages the switching between your mac and the PS and other connections you may have wired up to it (blu ray players, dvd players, apple TV etc)
You also have the option of using a 'sound bar' which has speakers and inputs built into one unit and runs along under your TV for stereo sound / virtual surround.
Some possible suggestions:
Receivers:
YAMAHA RXV373 Receiver
http://www.whathifi.com/review/rx-v373
PIONEER VSX-323
http://www.pioneer.eu/eur/products/42/98/405/VSX-323-K/page.html
You will need to find suitable speakers for the above. There are so many available which is dependant on your budget.
TV has Audio Out
If you are on a budget AND your TV has "Audio Out" via either red/white phono or 3.5 jack on the back then you can pass that into something like the Creative T30's so have both PS and Mac connected to TV via HDMI but the TV audio (whatever is playing on the TV) is passed to the speakers.
http://uk.creative.com/p/speakers/creative-t30-wireless
This would also work for Bose Sound Docks if you want a single wide field speaker, maybe a portable version too.
Also
The Creative T4's have Optical audio input too
http://uk.creative.com/p/speakers/creative-t4-wireless
So you can see there are many options depending on what you want out of it.
Anyway, whatever you decide you will greatly improve your sound field by adding your own speakers.
Anim