You're looking for a preamp. It's just that you're looking for one with a line out as well as a pre out. I have a similar setup to the two of you as I have 3 inputs (DAC, PS3 and CD player) and two outputs (line out for my headphone amp and pre out for studio monitors).
I got the Pro-ject Pre Box DS,
but if you're on more of a budget, you could get...