What improvements would I get with a "better" preamp?

@westcoastaudiophile OK, thanks for that. I thought I was going to have to stop listening to music there for a minute. I'm nor sure of the overall harm in my mistinterpretation of the sound quality of a given tube in my collection. I call myself an "avid listener", which I have been for over 70 years. I never intended to build my own gear or even to know exactly how it works. I do enjoy listening. Just so you know, you're not much fun. :)) Have a good one.

no problem bill, just look at the example of design issues of tube amp above (just added)!

@westcoastaudiophile When I look at that chart, I might as well be blind. I still have my ears though and I will continue to evaluate with them. I like to read about tests and I enjoy reading specs but my ears are always my final evaluator. I think yours are too, you just get hung up on measurements. You have the advantage or maybe the disadvantage of knowing the gear inside and out. I only have ears and a very basic understanding of stereo equipment and how it works. I'm OK with that or I'd have learned more, long ago. Sometimes, I do feel like I would enjoy a better understanding of the equipment and how it works but I don't have the patience or maybe even the ability to do so anymore. It's all good. Enjoy. I know I will. 

@billpete Tubes are NOS 6SN7 Tung-Sol grey T plates; separate power supply with NOS Raytheon JAN-CRP 6X5WGT rectifier. I think my system sounds good with the Mapletree preamp as is. No complaints from me. It’s just that the last two people I’ve had over for a listen, when I asked them, "What would you do to improve the sound", they both said they’d upgrade to a better preamp. So I am just curious what type of improvements would a "better" preamp get me, and possible suggestions as to which preamps would provide.

"@rockadanny  -  It’s just that the last two people I’ve had over for a listen, when I asked them, "What would you do to improve the sound", they both said they’d upgrade to a better preamp."

Can you share more - what was the basis for their comments?   Based on what, exactly?

I glanced over your linestage/preamp and almost asked early on what is wrong with what you have now? [you already indicated it sounds good, so what is it really]

Are these stop-in folks possibly confused by the minimalist appearance, or possibly not aware some of the best sounding boutique custom designer/builder gear is minus the "bling"? Have they tried your preamp in their systems to provide a more informed opinion, based on some type of A/B comparison?  Share more if you can.