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

I would say that the preamp definitely matters, and I am in the "cables do matter" camp.  I started with an MSB Discrete DAC and volume control.  My dealer lent me an ARC LS28SE to try.  I found it to be no different or extremely minimally better.  Then I put in an ARC REF 6 with a Shunyata Sigma power cord. Big difference in SQ, IMHO.  Then I replaced my Morrow Audio SP-7 speaker wire with Shunyata Sigma's.  Again, a very noticeable improvement.  Not night and day of course, but a definite audible improvement.  So yes, based on my own experience, a good preamp can definitely make a good difference, and so can good speaker cables.

 A good pre-amp should make no difference to the sound. If your power amp has a volume control, you can plug your source device directly into your power amp, so bypassing your pre-amp, (make sure your amp volume is turned all the way down).

 If it sounds better - ditch your pre-amp. 

Only DAC that I thought had a good volume control was the Lumin lineup. I used the Lumin X1 and the Leedh volume control. It was ALMOST as good as the volume control on my Benchmark LA4 (HPA4) preamp. All other DACs I tried direct to amp were not as good as a great preamp. You notice this at low volume when the soundstage collapses. The Lumin was not worse at low volume, it was just not linear in volume increase. Hardly an issue for most people. I no longer have the Lumin X1 and have 2 Schitt Yggi+ DACs (the OG and MIB) with the Benchmark HPA4 preamp.

Speaker cables are the only cables I spent high amount of money on. My gear does not seem to be improved by boutique interconnects (XLR + RCA). I love Audience FrontRow speaker cables and use them on both my systems. I have recently noticed a lot of people selling FrontRow speaker cables on USAM. People like to try different things but for me I am done with speaker cables.

BTW - Today, I only look for DACs WITHOUT a volume control.

My logic says if a pre is making your system sound better, then there's something wrong either upstream or downstream.

I'd rather have a good sounding amp and source with a passive pre.

I’m in the camp that everything matter within reason. If you have a Service Merchandise speaker with a VAC amp and a Nordost loom I think you not get the most out of the amp because the speakers are K-Mart.

If your room is less than perfect you will likely hear the difference a good pre can make but to me you're wasting money in fear of being beaten by the WAF stick.

You ultimately have to realize that you are playing at your own level and it needs to be fun.