USB Input on McIntosh C2700

Apple  makes a adapter,  that plugs into the iPhone and convert to USB, not sure if it will fit the iPad. Check Best Buy.

Check online auction sites for either the Wadia 170i / 171i or the Pure I-20. While no longer available new, these docking stations had a chip that provided the necessary electronic handshake to allow extraction of the digital stream from several generations of iPods using the 30 pin connector.
I have used the Pure I-20 and some old iPods in an office system for years. The I-20 was pretty inexpensive, even when new, and works fine. The Wadia dock was quite a bit pricier, as I recall.
Other than using one of these units, I think you’re pretty much restricted to the analog output regardless of what cable you find.

They also made iPod cradles just for this reason.

in theory, it should work.

Unless not supported. Specific use cases that wouldn't work would be in the owners manual.