As good as the 2496 was, for the cost of any 2 channel pre amp worth having, you could have a USB interface with two mic pre amps and zero latency direct monitoring. That's the direction I'd go rather than messing around with unbalanced phono/RCA inputs and outputs.
As for the choice of Thunderbolt, USB or whatever...2 inputs is an absolute dawdle in data terms so simple USB will be more than fine. I only worry about faster interfaces (I also have an ageing Firewire) when you get above 16 simultaneous tracks or so.