Any recommendation on specs for a secondary capture machine? If using a capture card does it need to be high end?
Depends if you're just recording to hard drive or if you're streaming to a site like Twitch. If just recording, you can just get a GTX 750 and a recent dual core (Sandy Bridge or later) and use NVEnc encoding and it'll be fine. If you're streaming, you'll want an Intel i7 to get a decent quality stream going because you'll need to use x264 encoding, and that takes a lot of CPU to do.
As for the expense/quality of the capture card you get, that depends entirely on the resolution and framerate you want to stream at. The bigger and faster, the more expensive it gets.