Connecting headphone and tablet to high end system

I have been sway from audio for some time but have recently set up my system. I realize a lot has happened in the last ten years with audio and a wondering whether I can connect my headphone to my spectral dmc 20 preamp using a headroom micro amp with a 3.5 to rca cable into the tape output. Also, can I connect with the same kind of cable my tablet to the tape input on the preamp to use Spotify as source?
Yes, you definitely can use the tape inputs and outputs for that purpose. However, you may want to consider using a better adapter to get digital out of your tablet and sending it to a DAC, rather than using the headphone out of your iPad. If you have a newer iPad, you can get a lightning to USB adapter and feed it into one of many USB DACs. As for the headphone output, the possibilities are limitless regarding headphone amplifiers and headphones themselves. There are many headphone amplifiers with RCA inputs such that you could use a standard interconnect to feed the headphone amplifier.
Whoops, perhaps your tablet is not an iPad. I do believe you can get digital out into a USB form on other tablets too. That is worth researching.