Congratulations on your new near fields. Brilliant aren't they?
I think you are on the right track looking at prosumer audio interfaces but I'm not sure the ESI represents your best option.
It's now quite old. There are many more up to date models on the market. Most of which will handle sample rates > 48Hz for example.
It doesn't have a volume pot. Best is to have 2. One for speakers and another for headphones.
It quotes output on TRS plugs but steadfastly refuses to mention balanced out which makes me suspicious.
Most competing interfaces offer more than 1 stereo out. 2 stereo out is good. So you can cue, run a simple subwoofer, satellites etc etc.
it is inexpensive though so if you do what Pleasant suggests and use the TOSlink out it will isolate the power supply grounds between your PC and amplifiers.
There are two other popular methods used to achieve isolation.
Galvanicly isolated USB implementation. Most pro or semi pro interfaces do this but not all. Domestic or audiophile grade appliances are less likely but some do. Unfortunately they rarely mention which are which. You can get USBground lift dongles quite cheap.
Balanced cables between both the interface and the monitors.
So take a look at these alternatives for not much more cash.
There is also a cheaper model, 2i2 with less outputs and a slightly more expensive one with more I/O options, the 6i6.
Steinberg and Roland among others make comparable products.
Slightly more money but worth it if you can afford the extra are the NI Audio 6 and MOTU Microbook.
Top of the range is something like the RME Babyface or SPL Crimson.
Here is a genuine pro grade unit that promises isolation.
Incidentally if you are really on a budget you could continue to use the on-board but pass the signal through something like this unit to achieve isolation.