Scott
Both players are virtually the same in sound and appearance. The 3.5 replaced the 3 because the 3.5 could be linked into a Hicap or flatcap which improved the sound.
If you have a tight budget...go for the CD3..it sounds bloody good and you will still have a player which is better that 95% of other players on the planet.
They are at bargin prices because all of the punters in the secondhand market are going for the 3.5.
If you can afford the extra cash....go for the 3.5 because you can buy a good second hand hicap for £350/£400 which will really improve the sound.
It is only worth going for a CD3.5 if you intend to buy a Hicap at a later date.
A CD5 is better( well some say its not) but more expensive......its all a question of how much cash you have got and where do you draw the line.
Make no mistake the CD3 is a bloody good player.
The problem with Naim kit is that it is so bloody addictive that you can easily get on the upgrade wagon and you need to make your mind up here and now what your future intentions are.
If you suspect that later on you will upgrade, then hold on, get some extra cash and go for the CD3.5. If you are able to resist the upgrade urge, stay with the CD3.
Which ever way you go.......you will have a good player that will last for years.
I notice that we are about 50 miles apart, I am housebound at present due to having had a recent operation on one of my shoulders, however, if you want to pop over for a listen to a player with and without a hicap...feel free to contact me.
Hope this helps.
Mick
