Agree 100%, a nice clean classic isn't a radio I would consider a candidate for excessive modification.
Now I'm not familiar with Sonars and I'm definitely not a tech so take this with a grain of salt:
To my ears some of the older radios have a much nicer audio than the newer stuff, they seem to let enough highs and lows in to have a more natural sound without going to extremes. With later radios and especially SSB rigs it seems that selectivity and efficiency became more of a priority and as such more effort was put into filtering out all those highs and lows. Now I wouldn't expect FM broadcast audio from it but I think plugging that box into the mic jack on an unmodified Sonar just to see what happens is a worthwhile endeavor.