Are Pre-Amps necessary?

Passive preamps do offer resolution but after that, not much else in my experience especially with the BeSpoke passive preamp ($10K).  It cannot compete with layering of the sound (vocals - instruments), no space between the instruments & vocals, placement within the sound stage, etc.  It just offers a flat sound stage by comparison.

Happy Listening.

need is a strong word.  
in my case the sound with a preamp in my system is on a higher level.  soundstage, speed, life like dynamics and energy, the sound accelerates much quicker making it exciting.  

Many believe having no active  preamp or linestage in the signal path is the “purest” appproach to home audio.  However, the electrical parameters of the cables themselves can result in colorations.  The balanced line standard Ralph often discusses provides  benefits in reduction of common-mode noise and in cable drive abilities (due to noise cancellation) but must meet certain requirements, which would be difficult to meet when using components from different manufacturers, because of differences in impedance and because not all equipment that has balanced connectors is actually a differential balanced design.  Some additional information for anyone who is curious.

A balanced transmission line consists of two conductors of the same type, each of which have equal impedances along their lengths and equal impedances to ground and to other circuits.
  

Circuits driving balanced lines must themselves be balanced to maintain the benefits of balance. This may be achieved by transformer coupling or by merely balancing the impedance in each conductor.

Compared to unbalanced lines, balanced lines reduce the amount of noise per distance, allowing a longer cable run to be practical. This is because electromagnetic interference will affect both signals the same way. Similarities between the two signals are automatically removed at the end of the transmission path when one signal is subtracted from the other.

Lines carrying symmetric signals (those with equal amplitudes but opposite polarities on each leg) are often incorrectly referred to as "balanced", but this is actually differential signaling. Balanced lines and differential signaling are often used together, but they are not the same thing. Differential signaling does not make a line balanced, nor does noise rejection in balanced cables require differential signaling.

In my experience, yes they are needed to get the best out of your music.

For my needs and wants,absolutely.  I can't speak for anyone else.