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

If a preamp is really all upside and no downside, as contended here by some, then the truly high end systems should have a couple of preamps daisy chained to get the best possible sound.  Odd that you never see that, even when funding is no issue.

Any time a signal is processed / amplified it is changed, unless you assume the amplifier is absolutely perfect.  Of course that is never the case.

If you have a deficiency in you system, like you need to add some tube warmth, or tone controls are required to balance the sound, then a preamp is potentially in order.  But note that the effect of the preamp is to alter the sound to achieve some end. 

I am not suggesting that there is no place for a preamp, but useful to be aware of what it is doing, both good and bad.

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.