Is dedicated PreAmp with Oppo 105 needed?

Don’t know much about “Sony ES TA-P9000ES 5 channel preamp

It was effective but prone to hum problems.  Not a  modern low-noise preamp.

 & how does it fare against modified “Krell S1200” or other Tube PreAmp.

Neither are those.  AFAIK, no one is making a multichannel preamp with performance equal to what one can get in a stereo preamp today.

@kr4 : So then the only option is to get a Stereo PreAmp with HT Passthrough.

Hopefully, the fronts speakers won’t be terribly loud or will have a different sound signature. 

Hello hitsofmisses,

     Wow, you've been contemplating this subject for over 5 years now.  That's amazing, you certainly have more patience and delayed gratification than I do.  I've read that's a good indication of being emotionally mature.
     But c'mon, don't you want to at least try out a good quality stereo preamp, with HT Passthrough, in your system and have some fun?  Your main speakers won't be terribly loud, for HT the relative volume of the fronts is matched to the other surround speakers using the setup menus on your Oppo.  The overall volume of your HT audio will continue to be adjustable using the Oppo remote.  For music, the volume will be controlled by the preamp's volume control setting or remote control if it has one.
     Do you have any good local audio shops near you?  If so, these dealers are a good source of knowledge and advice for suitable preamps tailored to your needs and preferences.  They often even also offer free home trials before you buy.
     I'm still using a combination stereo music and HT system but now use an Oppo 205 for surround audio (and to match my 4K video tv) and a separate Mark Levinson 326S preamp, with HT Passthrough, for stereo music.  I perceive a significant improvement in sound quality on stereo music played through this preamp versus the 205, but it's a $10,000 preamp new that I bought used for half price.  
     I understand your preferred price range is not this high but I'm not sure you would perceive a significant improvement in sound quality, versus your Oppo 105, using a more moderately priced preamp.  However, I think it's definitely possible you may perceive a significant improvement if you find the right reasonably priced preamp. 
     But you're not going to find a suitable preamp without trying several or more of them out in your system.  I strongly suggest you find a local shop that allows in-home trial periods on demo gear so that you can judge for yourself and start accumulating more experience.  
     I think this is a good solution for your situation. You've waited long enough, it's time to start enjoying improved stereo music sq or at least gain experience, and resolve your curiosity, if a separate good quality preamp with HT passthrough doesn't improve your stereo music sq performance.  Based on my experience and opinion, the Oppo 105 and 205 both contain high quality preamp sections that will be hard to top without spending big bucks.  

Best wishes,
   Tim

@noble100 : Thanks for the positive words of encouragement. But they’re quite far from reality. You can just call it my survival instincts. 😂

I know I’ll be entering years long war with series of battles & skirmishes with my wife at each conversation, get together, dinner, etc. when she realizes I spent another grand or a few on a piece of electronic equipment which she considers to be a ‘junk’.
I’m just thinking of those days (because I’ve this inner conviction that they’re definitely not far from coming), when I’ll be sitting in a corner licking my wounds, I don’t want to have any regrets about the decision I’ve made in my pursuit of achieving an elusive ‘Musical Nirvana’. In a way the delay is a representation of how long & tiring the war is going to be. 😂😂

The “good“ in “good quality stereo” is related to the risk you end up taking. But what’s the point of living if you’re not fighting for a just & noble cause. Sigh ...... 😂

Hello hitsofmisses,

     My suggestion is to talk to your wife, try to listen to music together and ask her for her opinions on the music and your system's overall sound quality. The goal being a hobby you both enjoy together, if you think that's possible.

Best wishes,
     Tim