Will a high quality preamp really make a difference in sound?? Also speaker cable

Additional processing will not necessarily negatively affect the signal. This is a misconception. And at the very least, positives may outweigh negatives.

Preamp without a doubt is the most important 

Clearly you should seek out the best engineering and scientific perspectives on this question which means you should choose a pre-amp that delivers exceptional measureable performance. There are so many exceptional performers out there. You can consult resources like Audio Science Review to learn more about amplification and audible thresholds. There are also useful notes on source switching noise and power-on behavior.

Professional engineering and science has not found much value in high cost cables, alas, but very high quality pre-amps for reasonable prices are quite easily obtainable.

Your system is only as good as your weakest link.  This doesn’t mean you have to spend gobs of money.  It means you spend on quality gear that gives you your desired sound.  

I think I would reframe the question.  Is a standalone preamp with lots of inputs necessary?  If you only listen only to digital then many DACs have well implemented preamps built into the unit (not in digital domaine).  If you listen to digital and vinyl as I do, some DACs have an extra analog input as does my MSB Reference.