Cute little thingies with luxurious design which belies their low-end status, these two STR are quite forgotten, just as the very rare "70" system from 1969 (TA-70, ST-70, SS-70).
Bigger in the same series, and Surround Sound compatible, are the slightly later SQR-6550 and SQR-6650 (1971) which had a very interesting grey/bronze lower panel and, mostly, QUAD oblige, lots of VU meters, as in the very rare and Godzilla-esque SQR-8750 lineup topper.
No high-end here, of course, no frills but a dair amount of music for the money - especially today.
We're far from the 1960s STR-6060 masterpiece, the 1970s Surround STR-7800SD monster or the well behaved and almost discrete STR-V7 series.
The STR-6046 adds a bit more more output power, a high filter switch, a speaker A / speaker B selector, a MIC mixing pot and, more importantly, the possibility to separate the preamp/tuner section from the power amp ; it is otherwise quite identical to the STR-6036.
Both can feed two loudspeaker pairs, both have MIC stereo inputs (in mini-jack style !) and both have a DIN rec/play tape terminal on top of the regular RCA.
There are later "A" versions of both : STR-6036A, STR-6046A.
The 36A has two buttons for speaker selection (as in the 46) ; the 46A has a bigger power section with an added heatsink that shows through the back plate but no speaker fuses - thank you Peter van der Waals for these details !
I have seen versions which are a mix of both non-A and A : a 46A with no heatsink but fuses, a 6036 with a heatsink etc. Plus the usual market differences : multi-voltage or not, AC plug or not.