
Wikipedia indicates that Wirrick was Sylvester’s guitarist and co-writer by 1976, i.e. before even the first album by Sylvester. It seems that by the time of the ‘Call Me’ album, Wirrick was doing a whole lot of songwriting (together with Jeff Mehl) and production. So I would guess he indeed continued his guitar duty too.
P.S. Also of note that according to Discogs, the credits straight up list Wirrick as ‘all instruments performed by’ (apart from some additional stuff on individual songs), which is quite impressive.

Just FYI, I’ve seen and heard a speaker looking like a tin can, sitting on the desk, perform very solidly — and I myself was using Sennheiser headphones and pretty respectable boxy speakers by that time. This was ten years ago. By now any little standalone speaker can probably outperform one embedded in a tablet.
Regrettably I don’t know any model names, might have to look for them myself sometime.