What is the size of your room and what kind of music do you listen to? Alot of people are liking the Topping products and that model seems to have some decent options. If your the DIY type, check out the ACA from Nelson Pass, low cost class A that will work well with Heresys in the right setting and listening habits. 

Would running something like a Topping MX5 bring any justice to the Heresy IV’s? Or do they really deserve a higher end Class A or tube amp?

I agree with wuzzzer. A new crossover, regardless of design, will NOT give you more bass.   Your pre-amp is very old and does not appear to provide a line level output to a subwoofer. The solution is to either upgrade to a newer pre-amp, or find a subwoofer which will accept speaker level inputs. These are less common, but available. You can connect the subwoofer via your current amp's Channel 2 or B speaker outputs (if it has them) and you'll be fine.   I own a pair of Heresy II's and while in the past I've been an advocate of adding a subwoofer, my recent listening is starting to moderate that recommendation. However, you will find a subwoofer does add an extra dimension to music if your tastes include bass below 50Hz.

😛   More than just the logo is different...    

i thank you all for replies   @Woofers and Tweeters i agree with. Will listen them for a while. İ am not and audiophilie and i cant understand if it needs maintanence. Maybe it sounds good to me but a professional listener may find problems. But for the difference to understand, i will keep them for a while as they are now.   mine is rectangular cup.   what do you think about crossover rebuild kit? Does it change sound or makes it became as new with original character?   @82 Cornwalls parallel conection? Can you show me a diagram of there is any on web.   ——/   my friend retailer is selling klipsch rw-12 sub. He told me To bring it home and try. Anyone has an opinion on this sub? Normally i want everything vintage, no digital era device. But for sub it can be modern.    if you say okay to rw-12 please tell me how to connect to my sony-ta-fa6b. İt has a and b speakers. Pre out. But no sub out. Maybe tape out?

I love the collection of tuners, the multiplexer looks new. Also thinking there are a pair of Heresy that would go great with the Pioneer receiver. All of that equipment is old enough and nice enough - have them checked out before plugging them in. You have a real treasure trove there. Lots of good advice above, enjoy the ride.

OK we know what the original bonafide Xilicas look like inside correct? I can take the lid off the one I got from Hong Kong. Will photo and post in the next few days...

I'm yet to see a Chinese knock-off of any audio equipment where they managed to make the logo appear identical to the original. I lost count of how many fake DSPs I came across over the years. Ebay had many of them for sale. U87 mics and other gear as well.   Attached are pictures of the original xilica units. It would be great to see the inside of the Chinese units so we can compare. There are too many for sale at the moment when Zilica said that they discontinued them.

Love the string arragement on this. Such a classic song written by Jon Randall & Bill Anderson    

Post pictures of the variant Louis...