First, I'd send your wife back with the "15" and tell her to get a "16", and...
accept no substitutes!
My friend, tho I think there are numerous heads who would read this post and want to snap that 488 up asap, if it were me and these were my only two machines, I'd keep the 488.
My reasoning is this: I critique
the MR16HD (and the whole class of similar units) as inadequate in what's often referred to as "front-end" mixing. This is the mixing of inputs to busses, then subsequent assignment of busses (not inputs) to tracks. Any 488 or mid- high-end Portastudio does this intrinsically in the design. They record in buss mode as well as direct.
The MR series, f/i, just assigns inputs-to-tracks, with no capability to route more than one input to a single track. There is no front end mixing, no buss-mode but only direct-in configuration.
When I record, I'm accustomed or prefer to submix inputs to busses before assigning to tracks. That enables me to (f/i) mix a DI line-in guitar with a close-mic of the guitar, mixed together and routed down to 1 track, or route any number of drum mics into a stereo submix, or any number of common things like that. Front end mixing is an every day primary concern in the way I produce music. The capability of recording in buss mode vs direct mode only goes hand in hand with that. The MR16 and e'thing like it has no buss mode & [IMO] begs the issue of needing a front-end mixer.
I know with
'wow-its-digital' theres a different philosphy,... that you're not as limited with track count anymore, so why submix on the front end, but instead just plop each input on it's own track and mix (or bounce tracks down) later. I hear that constantly as the counter argument why something like the MR16 doesn't need a full functioned mixer that mixes signals going in both directions in the recording process. Maybe I'm old fashioned or old school, but I never got that mode of thinking or got onboard with that idea.
What you have on the MR's and e'thing like it is an input-to-track architecture with a playback mixer. Maybe I'm spoiled with my Tascams and take full functioned mixing on an-all-in-one unit for granted. On balance, I feel the MR's (etc) are sorely lacking in the mixing department, specifically on the front end side of the recording process.
I think it's best to keep the 488 as it will prove invaluable as a submixer, even for a soloist or producer working in a small setup. The issue of submixing is something the MR16HD falls flat on entirely, and the 488 would complement that well. The MR16 is 4-input/4-simul and the 488 is 12x4 (4-buss) mixer, so I think that's a good fit. The 488 could prove very useful as your recording technique evolves, but as always YMMV.
8 channels would be awesome to work with, in my new "projects".