Help a guy out? Renovating home theater system after 10 years and have a few questions.

The only downside of the receiver is that it is old fashioned and does not support UHD video and some modern formats. So as long as you do not upgrade the screen to UHD it should be fine, however.
Good modern AV receivers are not particularly expensive compared to the cost of good speakers, but make sure that if you decide to get a new receiver it has plenty of power (the more the better), also with all channels driven. That puts a big demand on the receiver's power supply, which happens to be the most expensive part of the unit.
The weakest part of the audio side of your set up is not the receiver but the speakers. I can well imagine that you feel the sound is not big enough, let alone good enough. Unfortunately speakers are also by far the most expensive part of a system.
The biggest impact on the size of the sound in HT would be to replace the subwoofer with at least two modern ones. See here for why you need multiple subs: http://www.acousticfrontiers.com/20101029using-multiple-subwoofers-to-improve-bass-the-welti-devanti...
Brands to consider would be SVS or Rythmik, but there are other good ones as well, particularly at a bigger budget. One interesting option would be the Audiokinesis Swarm system: http://www.theabsolutesound.com/articles/audiokinesis-swarm-subwoofer-system/
In all cases I would suggest a dsp room equalization system as well, either one that is built into the receiver, or an external one such as the DSpeaker Antimode 8033.

Vasubandu I would start with a reciever from Anthem. The same company that makes your speakers. I am using a 58 inch Samsung plasma still since 2010. I was reading an article in Widescreen Review from Joe Kane about the UHD 4K displays, and the manufacturers are still using different standards. I would strongly advise you to wait a little longer on the display. The content is not there yet either. I have gone crazy on the audio end and got an Anthem P5 Statement to drive my large mains and surround rears. I built a center channel to match since the factory no longer exists. All the same drivers and crossovers. Tweeters and midrange all at ear level in the same plane. Using 2 Nikko Alpha 440s to drive smaller height speakers for Atmos. My large speakers are ADS L1290/2s and small speakers 4 of them are ADS L300s. I am using 1 HSU sub VTF-MK4. All my stuff was used and I purchased the speakers on Ebay and Craigslist. I had them all rebuilt by Rich So. The P5 I got used for half price of a new one. I bought the subwoofer online and had it shipped from the factory by UPS. I had the 2 Nikkos rebuilt as well. I bought an Anthem AVM 60 new at the dealer where I got the used P5. I have been into audio all my life since a teenager, now 61 yrs old so I know my way around setup and calibration. Even with yrs of experience when I ran the room correction ARC, that was in the preamp the sound was vastly improved. I used to use Spears and Munsil 2nd edition disc to calibrate the sound with a sound pressure level meter but the ARC system with the calibrated mic is much more accurate. Get one of Anthems recievers and you will be very happy. Get as much power as you can afford. Go slow as the budget allows but get good quality and it will last decades.

OLED is the latest screen technology and it every bit as good as plasma but has far better resolution than plasma every achieved. My TV is the LG 4K OLED 65 inch and the quality is stunning. I checked it with professional photos on a memory stick and it has superb colors without any if the horrible backlighting of LED or LCD - superbly accurate.

vasubandu,

     You have some good equipment to get started with if you want to cobble together a good ht system. 
     However,  I think you need to decide what your goal is for the final result.  Do you want a  good ht system that utilizes as much of your existing equipment as possible to save some $ or do you want a very good ht system that takes advantage of the latest technology?  No matter which route you decide on, you'll then need to give a budget estimate in order to receive useful suggestions.
     I  know I, and believe most members here, would offer different suggestions based on your goals and budget.  
     I think I can give you some useful advice no matter which method you decide on but I also need your budget to better tailor them to your expectations.

Thanks,
  Tim
     
     

For the OP, why not get separates for electronics?  Get a nice powerful multichannel amp that will really make the speakers you use sing before you decide to replace them, and add a processor that will do all the new things that your present pre amp section can’t do. Then as technology changes you can change the pre amp but leave the power amp in place