Bassot ›

I've used the Ampeg SVT tube DI for quite some time and it performs very well.
It has a somewhat sweetening effect thru the tube but it's pretty subtle. But if you have hot pickups and don't use the pad, then the tone gets sweeter of course=) . I've also used it on guitars in the direct mode and it works.
 
For me the thing is that a good DI box is superclean, not adding anything nor taking anything away. And these mic preamps and tube-thingies are ways to add something to the signal, sweetening things.
 
I've also started building a G9 tube preamp which should be in the same league soundwise as the high-end tube preamps
 
And for home practicing and recording i'd use just the cheapest stuff that works. I'd use maybe the bass v-amp or such. It has the modeling stuff but it also can convert your signal to line level so that the levels match between your bass and soundcard.
 
And for VSTs, the best price/quality ratio is with Voxengo Boogex and some nice free impulses. Ampeg SVX is good but not worth the price and the hype IMO.