The Hofner is just over 3.5" deep and you can play it unplugged with roundwounds if you want. IT does have a very acoustic sound due to the spruce top and the floating bridge. Many people prefer them with tapes or flats because it produces a lovely bass tone with them. However, IF you NEED a dual purpose bass that can perform acousticly, then the round wounds produce more volume acoustically.
I dont have a Kay, sorry. Wish I did. However, my Dean Stylist is a hollow body with a fixed trapeze bridge and it is a medium scale. The body on it is about 3" deep. The Dean Stylist has way more thump, but does not have nearly the amount of acoustic timber that the Hofner does. I think that the difference in the bridge makes for a good part of the difference in sound. Also, while the Dean is hollow, it is not an archtop and it is not a spruce top.
I found a few 500/5 samples for ya. Hope you find them useful.
First, the best known 500/5 as played by Stu Sutcliffe: ON this song, you can actually get a good perception of what a 500/5 was sought out for back in the day. http://www.youtube.com/watch?v=bpDGH7hltIU
Next the official Hofner demo with factory strings. [sarcasm] BARF [/sarcasm]
No, I don't care for this example, but it is a tone you can sqeeze from this Hofner if you really wanted it and I'm all for truth in advertising.... http://www.youtube.com/watch?v=PvX0MK1y_Rc
Next, my favorite - Ralf Gauck doing a classical peice on tapewound strings. I contacted him and he told me that his model is a German made prototype of the re-issue. He wired his pickups directly to the output - bypassing the control panel. Take a listen.... http://www.youtube.com/watch?v=iHhyy16kEM0
Last example, some knuckle head putting one of the original '50's models through its paces. Not what I'd do with it, but for a sound sample, it is somewhat useful... http://www.youtube.com/watch?v=G8SsRjSPpFA
Keep in mind that the control panel on these 500/5 models is wired such that the two pick ups are out of phase. The knobs are a volume control for each pick up. Two of the switches are on/off for each pick up. If you have both pick ups on, then having both volumes up full actually kills most of the volume and tone. You get a thin reedy sound that I don't find useful. So you either go with one pick up on or blend the two volume pots somewhat to find a tone and volume that you like.
The third switch routes the signal through a resistor to kill off some of the highs. It says "Rhythm" and "Solo". The Rhythm setting drains off some of the highs and it is not as loud so most people keep it at the Solo setting.