That Fisher receiver looks like one of the company's high-end FM integrated stereo receivers from about 35 years ago, which used the same preset tuning system. (The radio's preset tuning works exactly like the five-button presets on car radios as well.) I think this was probably the best (and maybe the only) way to have so-called "memory" tuning at the time; these radios were made some years before the 32-station (more or less) preset solid-state memory tuning systems in today's bookshelf audio systems were popular or even thought of. A distant cousin of mine had a Fisher integrated receiver in the '70s which had this type of push-button tuning, and it sounded great. No wonder. Fisher was synonymous with great hi-fi sound from its beginnings (remember their "Studio Standard" line of hi-fi gear in the late '60s-'70s?), and the prices of their equipment proved it, so I am not the least bit surprised that your Fisher "micro" receiver sounds as good as you say it does. I would fully expect Fisher to have built its hi-fi radios to meet much the same if not
the same very high standards as its high-fidelity systems.
I would put your Fisher receiver in a class with Zenith's best table radios of the 1960s. I don't know how large the speaker is in your set, but Zenith's C845 has an 8" and a 5" speaker for lows/midrange and highs, respectively, and the K731 has a 2-way speaker system with a 5x7 oval speaker and a 3" (more or less) electrostatic tweeter for the same frequency ranges. (I can vouch for the sound quality, as I have a K731 and a C845 that sound absolutely fantastic;
but then again, that was the way Zenith built their high-end radios and hi-fi gear 45 years ago.) If your Fisher receiver has provisions for one or more external speakers, I'd try hooking one up. If the set sounds good through its own speaker, it will very likely sound even better (especially in the bass range) playing through a larger one.
I would be careful, however, that the speaker connections do not short against each other or to the chassis; this could cause severe and permanent damage to the radio if it has a "hot" chassis. This warning applies to RCA's later-model solid-state TVs and, I would think, should apply to solid-state radios as well, again if the latter are designed such that the chassis is connected directly to one side of the line. Tube-type AC/DC radios and small portable televisions of the '50s through the '70s or so were almost universally designed with this type of filament circuit, but the hot-chassis design is fairly common in some newer solid-state TVs such as RCA's CTC-185. (The service notes for my own CTC185 mention this potential hazard and advise the user to connect external speakers to this TV by means of a VCR or an external amplifier system which is in no way connected directly to the set's own speaker.)
However, to be on the safe side, I would be very careful when connecting an external speaker to
any kind of solid-state table radio unless it is known beyond the shadow of even the most unreasonable doubt that the radio is transformer-powered. Most battery/AC sets use small transformers in their AC power supplies these days, but some AC-only table models might have power supplies that use the chassis as ground return. The latter are the ones to be wary of as far as hot-chassis problems are concerned. Of course, as I mentioned above, if your set has an RCA jack or similar for external speaker connections, so much the better; just plug in your external speaker and you're good to go.