My laptop sadly doesn't have SPDIF in.
I found a product called U24 XL by ESI Audio, but am wondering if the fact it's relatively cheap would have a consequence on the quality of the signal's transmission.
Otherwise, I could try to find a used USBPre.
Voltronic, if you have any experience with Sound Devices, could you say the preamps are similarly quiet in the Saffire?
That ESI does not have mic preamps, so if you're looking for that I'd look elsewhere.
Back to Focusrite: it looks like you'd want the Scarlett 6i6 as it has SPDIF. I don't have any experience with Sound Devices, but I don't think you can really expect a $250 interface to compete with something 10 times as expensive. I can tell you in my Saffire interface, the preamps are still pretty quiet when I crank the gain all the way up to 60dB.
If you need the preamps to absolutely be as good as the SD, then you need to use SD preamps and go with H20's suggestion, and use your SD as the pre and D/A, feeding SPDIF. You could then get that ESI, or any other cheap interface with SPDIF input.
Personally, I would just get the Scarlett 6i6. At $250, it's got SPDIF in/out, so you have the ability to run your SD into it or use its built-in preamps. You also would be getting a higher-quality output device than the built-in sound on your laptop, balanced in/out for connecting to pro monitors, etc.