I think the reason no one has answered your post yet mate is because of your requirement for both TRS (or maybe TS??) jack outputs and optical co-ax in.
Generally nowadays TRS jack output comes on pro and semi pro audio gear. Usually input via USB 2.0. If it has balanced out the need for optical in becomes redundant. Anyway most USB interfaces are either already isolated by design or have a ground lift switch. If they don't and you do have a problem with your system earthing you cannot fix normally an after market isolator is very cheap and effective.
You can also buy very inexpensive optical S/PDIF > analogue converters. The FiiO D3 is a good example and only costs ~$30.
So assuming USB will do this MOTU Microbook would suit you perfectly for $300
The main reason being that it comes complete with an excellent EQ and effects package called CueMix. Take a look at the spec and pictures in the link. It's far, far more sophisticated than a simple graphic equaliser. You get 7 band parametric EQ on all input, output and mix channels via a simple to use and pleasing to the eye graphic interface. There are also 2 compressers and reverb, echo should you find a need for them also.
The headphone output impedance isn't quoted but it's a new unit so it probably has a low enough figure to cope with headphones designed for iPod generation as well as pro grade. Check with MOTU direct if it could be a dealbreaker. NvAvGuy recommends using something like the $20 FiiO E05 as a ultra low output impedence socket and volume attenuator.
I know it's not exactly what you wanted but it does have the best EQ control of anything within your budget and in the absence of other suggestions???