Showroom performance?
I would think very hard about replacing a KLN89B, true the KLN94 has a few more functions and a map but the system is a full approach aproved BRNAV system.
The thing that it lacks is a good display to me the way to go is to let the unit drive a display such as the new Sandel EHSI. this will give you a Nav display almost to the standards of a modern airliner without the micky mouse road map that clutters the Garmin.
If Eurocontrol ever get there heads out f the sand with traffic info & weather radar data links via the mode S you could display this as well.
In by opinion the KLN89B and Sandel EHSI offer real usable "in the air" performance at a resonable cost rather than a moderate size map that is of little practical use in the air but looks very good in the showroom.
Garmin have been very clever with the GNS430 in that it delivers COM/NAV/GPS in one package at a time when the world was full of ageing KX170 radios that are only fit for the scrap bin but it is no longer the best option in terms of ease of use and value for money vs performance.