What can I improve in my audio system for better s


I have lossless FLAC music ripped from cd's and music I purchased from HD tracks, I am using Macintosh MX 121 processor, Krell S1500 7 channel power amp, 7.1 SYSTEM, B&W 802D speakers for front and center, Monitor Audio for side and rare channels, Crystal and Audio Quest for interconnect and Tara Lab for Speaker cables. I am using JRiver to play this music from my computer, which resides on Lenovo Q180 small foot print PC with build in HDMI which is connected to my processor via this HDMI. I don't know why but I feel that this PC is the least expensive equipment I have, and is the weakest link in my entire system. There is nothing wrong with the system. But, it always bugs me that I can improve this weak link. I like the fact that while playing music I can see the album cover and track information on the monitor. But still I am curious to know, if possible, how I can improve the sound quality. Since I have a McIntosh processor with built in DAC, I don't want to add another DAC (by the way I tried using Moon DAC, it was no-ware close to McIntosh MX121, ended up selling it on eBay). I am not even sure, while using HDMI port does better sound card matters? Or can I enhance anything in my system to improve the sound quality or am I looking for unrealistic Magic? When I purchased this system, my friends were so surprised from the money I spent, there first question to me was "Does singer comes out of these speakers to sing for you?" I guess that's what I am expecting; I believe I am missing those emotions that we get from live performance.

Need a professional advice, please help.
trcns
I will add the pictures. Only time I visited the dealer when I was shopping for speakers, I listened to YG and DynAudio along with B&W. All the rest of equipment I purchased is based on reviews of the equipment. Monitor Audio reference speakers were my original speakers before buying B&W 802 D's last year, so I moved them as side channels, I feel that they timber matched very well. Music sounds very very crisp and clean. I never compared my system with other systems. I never had an opportunity to spend hours and hours at dealers location and now little by little all these Hi-End audio show rooms are disappearing. It's just a bug in my head, always thinking is their a better software than JRiver? Is there a better way to connect computer to my Processor other than using HDMI? Should I buy a better HDMI cable? Or a better sound card? Should I change my hard drive to SSD drive? Will it matter if I change my sound cards setting from 24/96 to 24/192?
I cannot provide you with any specific expert help here. However, improving sound quality is a slippery slope. I know from experience. Make one change to your system at a time and then give that one change plenty of time in order to learn what, if anything you have achieved. Then you can move on to a different variable in your system to change if you are still unsatisfied. Try to be patient with each change.
You can improve your audio system with latest technology such as "asynchronous" DAC. Sample rate conversion of all inputs, which are re-clocked, re-timed and up-sampled. You can spend $500 for the new ZDAC2 or $5,000 for PS Xtreme.
Honestly, for surround sound, you seem to be working with all good stuff. Not bad for two channel either. If the best 2-channel sound quality is of interest to you, you could probably do some things there for comparison.

Again it all depends on what the perceived weaknesses are and what the target is.

Definitely good advice to have a roadmap up front to get where you want in steps, but only change one thing at a time, one step at a time, and take plenty of time to assess each step along the way towards the goal.