The passive bass needs active DI thing is a bit of a falacy, in truth both work well for either. The fact that they are active or passive makes no difference, the only critical factor is the DI's input impedance, and the bass' output impedance. 'Vintage' basses with old pickups may well have a generally larger output impedance and as such may well do better with an active DI, where its easier for the manafacturers to give it a high input impedance, ie you can avoid a missmatch. Generally though, both will work fine for anything.
Its true that most DI's, especially most passive's, will colour the tone very little, but they WILL send the signal through a transformer which WILL colour the sound somewhat. Even top transformers like Lundhals and Jensens change the sound a bit, and its these characteristics that people seek out and take preference too in passive DI's. Like all variables for recording gear, the difference will be slight, but recording is ALL about the details so you need to learn to hear the differences to get the most out of your gear.
Yup, you'll need to come out of the balanced, xlr, di out for the signal to have been 'DI'd'. The thru or link socket is simply hardwired to the input socket on most DI's and as such is no different to running a jack directly to the interface. The DI simply splits this signal off in between the input and thru jacks, sends it to a step down transformer in a balancing circuit and comes out of the xlr out. Passive DI's are VERY simple devices and it the only real variable between the different makes is the transformer used, along with extra bits and bobs like pad switches etc.
A passive DI will reduce the level of the signal post transformer, so its customary to send it into a mic preamp. Is the 1/4" input of your interface listed as being a mic pre as well, or does it have an xlr in? If not you may find it does not have enough clean gain to make a passive DI worth it.
Is it a little guitar style interface like the line 6 stuff? If so the 1/4 input will likely have enough gain, but will probably already have a high enough input impedance that you don't need to use a DI, that said the colouration of the DI might still be desirable and its always useful to have one around.
Active DI's come in many more flavours, so its more of a item by item consideration, simple ones like the countryman may still reduce the signal by a bit (I'm not sure about this) wheras fancy ones like the avalon u5 will be able to give as much or as little gain needed to go into a mic pre OR line input at a good impedance.
Hope that helps a bit,
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so here it is. I am also looking to play guitar through my DI box to use with Guitar Rig 4. Do i need any special considerations when looking to get a DI box for both Bass and Guitar? 
