My very old Nytech ca252 has a pre-out/power in socket, and I've just found out that Nytech's current integrated, ca352, still has one - but at £2k, might be too much.
This might be obvious, but an amp with a 'tape monitor' switch will do what you want - via tape out/tape in sockets - 'monitor on' just internally disconnects them. My
dad had (an even older) Leak stereo 30 plus, that had this feature - from the 60s, when tape was popular, but probably quite rare today....
khozmo passive pre/nytech ca252/cxa252 amps, arc 101 speakers
vinyl: --- lp12/kore/lingo4/ekos2/dv 10x5/gs accession
digital: --- caiman SEG/allo digione, synology nas, rotel 965 cd