Speaker level output vs line level output are they the same thing or what?

[Rolex Snob]

I have to rant here, I can't seem to find any good information on this topic. As a car stereo novice I am trying my best to put some concerns to bed but what plagues the car stereo world is there is a wealth of conflicting and flat out incorrect information out there.

My amp is dead, I want a new one. I am trying to decide on a new one...

My #1 goal, I don't want any converters other than ones built into an amp.

My previous system had PAC-SNI-35 boxes, they are two channels each so I had two of them. They are advertised as LINE OUTPUT Converters; I was told these are for connecting directly to speaker level. An example of a proper installation I would assume is when I am splicing into factory speaker wire off the stock amp/head unit before the speaker itself. This is garbage, why anyone would do this is beyond me.

The reason I was told this was not the solution was because I removed my factory amp and needed to convert directly from the OUTPUTS of the factory head unit directly to the INPUTS of an amp instead of RCA ouputs I had 4 wires that needed to be coverted to RCA (not to be confused with the wires connected to my speakers).

I was told the SVEN4 was the proper device for this, application. The SVEN4 is advertised as a "sound interface device" and from what I understand is meant for converting the actual speaker wire outputs on factory head units to RCA. I am not splicing into the speaker wire that is already going to the speakers.

Now, what confuses the ever living shit out of me is how this is described. I know there is a difference between the two devices (SNI35 & SVEN4) because I have heard it. It is night and day, so I want to make sure this is done right. I will not tolerate gimped sound anymore and want to purchase the correct amp for my situation.

I want my factory speaker wires going to my speakers, I will not touch these. Since my factory head unit amp in my 2002 X5 is disconnected I have 4 output wires (I wont call them speaker wires because this is the main area of confusion for me, I will call them "outputs using wires that are not RCA's"

I know I sound like an idiot, it's because I am. I don't know the fine details needed to survive in the non-ghetto audio world but I have little trust in my local installers because they started out giving me speaker level crap. I hate it, I would rather support terrorism than give another penny for a product like the SNI-35.

Please enlighten me here? Is anything I am saying correct?

Is there is a difference between line level and speaker level?

What amp would you recommend? Please don't say anything that only has RCA inputs because that is not adequate.