Start with the level of the source
A cartridge signal needs phono gain and RIAA equalization before it reaches a line input. A CD player or other line-level source belongs on a line input. Identify the source output and amplifier input first; a connector match does not tell you which stage is needed.
Match the cartridge to the phono input
Moving-magnet cartridge -> compatible MM phono stage -> amplifier line input. Suitable low-output moving-coil cartridge -> matched MC step-up transformer -> compatible MM phono stage -> amplifier line input. A passive transformer increases voltage but does not apply RIAA equalization. Compare cartridge output, recommended load, transformer ratio and phono input gain before choosing.
Select sources and set listening level
The Reference Passive Controller selects among line sources and attenuates their level without added voltage gain. Match source output, controller loading, amplifier sensitivity and cable length together. An active line preamplifier can be appropriate where the system needs gain or a different output-driving capability; check the chosen build's specifications.
Headphones need their own output match
Choose a headphone output for the actual headphone impedance and sensitivity. The Tube Control Amplifier targets high-impedance dynamic headphones; compatibility with low-impedance or planar headphones requires the relevant output and load specifications. A phono stage or ordinary line output is not a substitute for a headphone amplifier.
Send one stereo source to three destinations
A stereo distribution buffer takes one stereo RCA line input and supplies three separately buffered stereo outputs to compatible destinations. It distributes the same source; it does not choose among sources, mix them or replace a listening-volume controller.
Put recording and monitoring in the right loop
Source -> recording buffer -> recorder input; recorder output -> monitor return -> listening system. A tape-monitor arrangement selects the source or recorder return for listening. Actual off-tape monitoring depends on the recorder's capabilities. Confirm input/output labels and levels, and avoid routing the recorder return back into its own recording input.
Place vinyl filtering after the phono stage
Cartridge -> phono stage -> line-level subsonic filter -> downstream line control or amplifier. The selectable filter addresses low-frequency content in a compatible line-level vinyl chain. Review the selected filter settings and response rather than assuming a particular cutoff or slope.
Choose optional processing deliberately
The Harmonic Stage offers a tube line buffer with bypass and selectable operating modes. Use the documented levels and behavior of the chosen configuration to decide whether it fits your system. Tube processing or a passive signal path does not by itself establish better sound.