Dear friends I am interested to upgrade my caps in the tube preamp from Audio theta tin foil 3uf200VDC to Miflex1uf 240VDC copper foil what are your thoughts will reducing the value to 1uf affect the bass and frequency response or should I go with a higher value than 3uf  
You can change the value of an output coupling cap and do so safely and do so to better effect. But, as a general principal you want to stay near tolerances as designed.
Sometimes people violate rule no 2 above because they want to better match impedance between amp and preamp. Manufacturers usually try to pick a level that will match with a larger number of combinations yet you can customize this so the gear mates better. There are good calculators out there for this purpose.
I hardly ever check this forum any more but I did today and I read this entire thread.  And it reminded me why I don’t read threads here.  Same people arguing about the same topics, over and over.  Don’t you get tired of this?  You guys need to move on!
As far as what brand capacitors to purchase, the two choices for us were V-Caps and Audio Note.  In comparing Milflex copper to V-Cap Oils, we preferred the V-Caps.  The ODAMs are an excellent option and the Copper V-Caps are excellent but expensive.

Happy Listening.

I have a question, about, the cap located in this crossover. You know what's going on.

Can I use directional caps in this crossover?  Hooking the + side of the cap to the incoming  + signal and the - side (marked) in the direction towards the speaker + terminal? OR in the case of C7 where it is going + to -?

Could there be an issue for the amp in any way?

I'm not try to set you up either.. LOL I'm asking because I've used directional caps in crossovers (Vishay 160v) with wonderful results.

Actually one of the most neutral caps I've ever used other than Clarity.

I've found that resistors have a signature too.. I'd like to see some studies on that. 

The exception a LOT of boutique caps. Mundorf is about as colorful as they get. The exception being the little white Classic 630v..

What say you Mr cakyol, I was just wondering, why? Bi pole vs polarized, would it make a difference in a passive crossover? I'm cheap when it comes to 400.00 usd caps that are on the low side.. I'm a 4.00 cap guy.  40 cents is even better. :-)

Russian surplus PIO. 2.00 dollar special. Why not they sound really good?

What about Russian surplus, ANYONE? Who has used what?