Sending USB and audio to LCD through thunderbolt

Okay so a couple of things are at play here. First of all, DVI doesn't carry audio - so even though the Mac's Thunderbolt port is capable of sending audio, when you convert it to DVI that audio stream gets lost. This can get confusing though, because it is possible to send a HDMI signal over a DVI-D cable, which will carry audio. But that's technically not a DVI stream any more.

A DVI-D source can output HDMI signals including audio (e.g. ATI 3000->series and NVIDIA GTX 200-series).[9] Some multimedia displays use a DVI >to HDMI adapter to input the HDMI signal with audio. Exact capabilities vary by video card specifications.

Source: Digital Visual Interface article on Wikipedia

The next thing is whether or not that port is an Input or Output. I've got an LG monitor down the end of my desk that has a 3.5mm Jack on the back, but it's an output. Meaning if you plug in a source that supports audio (in its particular case, HDMI) then you can pass that audio out to a set of desktop speakers. But it doesn't have any built in.

If it is indeed an input, you just need a 3.5mm to 3.5mm audio cable, and connect the headphone output of your MacBook to the speaker input on the monitor.

Something like this would do the trick: 3.5mm Stereo Jack Cable on Amazon

The upshot being, you can't do audio and video over DVI connection alone.

Officially your MacBook Pro is only capable of simultaneously outputting a video feed to the internal display and a single external monitor.

However, there are a number of USB display adapters that will allow you to support a second external display.

USB Display Adapters

These are USB to VGA or USB to DVI adapters. Some of these support up to a maximum resolution of 1920x1200 or 2048x1152.

These three are guaranteed to work on Apple Macs and support a maximum resolution up to 2048x1152:

1. Kensington Multi Display Adapter USB 3.0
2. IOGear USB 3.0 to DVI External Video Card
3. OWC USB to DVI/HDMI/VGA Adapter

These adapters work in by compressing and decompressing the video signal in order to utilise the limited bandwidth provided by USB 2.0 or USB 3.0.

However, you should be aware that there are limitations to USB Display Adapters. Namely they do not support OpenGL 3D hardware acceleration and you are likely to notice a lag.

If you're intention was to use these for gaming or animation/video editing, I'd say forget about it. But with your music production software it may be fine as the emphasis will be on the audio side of things, especially if you keep your graphics intensive work limited to the other display connected via the Thunderbolt port.

As far as how well a hub will go trying to connect to another display as well as your MIDI keyboard and a mouse, your success will depend on the quality of the hub and ensuring that it's also got its own power source.

A better option may be to also get a hub that connects to your Thunderbolt port that connects the display and also provides an additional USB port for example.