GTX 750 Ti is not the best GPU you could get for gaming, and combining that with a Xeon would be imbalanced.
Apparently
Steam in-home streaming natively supports NVIDIA hardware encoding so you definitely do want an NVIDIA GPU. Presumably enabling this will considerably lower the CPU requirement, so your best bet is to buy as powerful an NVIDIA GPU as your budget allows, with a CPU that won't bottleneck it. E.g. i5-4460 + GTX 970 (for the streaming PC, i.e. the one you use to actually run the game. The requirements for the client PC are
very modest.)
Also with NVIDIA hardware encoding, you don't really need much of system RAM, 8GB should be fine.