Yes, both cathode resistors R1 and R2 can be replaced with CF-type current sources.
The circuit shown is not a tape loop, it's a buffered tape output. That is, the tape out is the unattenuated signal from the selected source (phono for example) The main output is the same source, after attenuation by the volume control. You'll need another set of RCA jacks and a switch to connect the volume control to the equalizer instead of the phono. I assume you know this, but just in case someone finds this thread in a search I thought I ought to mention it.