Chains and signals

[vitolanzafame]

I was wondering if someone could help clear up some fundamental questions that i've asked lots of people in the recording business but without getting concrete answers.
Its to do ultimately getting the most faithful and pure sound possible.

I have an Mbox mini.
I was going to invest in a nice DI box like a Radial, and also a half decent mic pre like a focusrite ISA One.

But then i thought: the signal from my nice DI box (of say, a bass) is then going to go into the line in of my mbox, and then through the converter in my mbox. (Not to put the mbox down, but I don't know how high the quality of its converters and pre amps are.) So is my mbox essentially letting down other high quality elements in the chain (mics, mic pres, DI boxes etc) ?

Is it pointless to invest in great mic pres and mics without having really good converters and inputs? (and on this point, is the DI input in my mbox also a pre amp stage which colours the sound, or is it just a transparent DI?)

I know the answer is often "if it sounds good then use it". I do think the mbox sounds good. But then i hear something which is on a whole other level, and I'm basically trying to get as close to that as i can, but want to understand which elements i need to be spending on (and not potentially wasting money on)

I hope someone can help with some of these points!

thanks very much

Tom