Ossidian

I only use 15" woofers. Adding a second 15” Hawthorne Audio Augie up top to increase bass response, dynamics and to load the room top to bottom. This really makes for a big improvement.

Could not disagree more. My OB speakers completely disappear and there is no hole in center stage. Everyone has opinions and my 40 years of owning 100's of speakers and owning a High End store for 25 years tells me different. You are entitled to your opinions but they are not necessarily facts. After seeing your system setup tells me everything I need to know about your opinions lol.

On my OB Hawthorne Audio Rainier MK III I find 2" toe works well.

Good article on speaker basis some may find interesting. Speaker Off Axis

Lol. The amp is on 2" acrylic with 2" footers. The DAC is under 3" footers. The class D amps do not give off any heat on the bottom. Appreciate it though.

McIntosh MC2000 tube amp direct to McIntosh MDA1000 DAC. This is the way I like to hear my tube amp mostly.

What I would have given to have met Saul Marantz. What a legend Saul is. I still have my 10B tube tuner.

Yes, but it is $500 and you are right it is still a good value. Old stock A-9010 represent a great value.

Looks like the tech installed some nice Russian and Hovland caps in your AP-900. It's amazing how swapping tubes affect the sonics. The AP-900 is quite a nice unit indeed.

True, if you are bypassing the preamp section of your integrated the Mapletree preamp tubes would be best to concentrate on. Without seeing the schematics on the Ap-900 I have no idea what role the 6N1P play in the integrated. I have searched the internet but found no information on the AP-900.

If you are using stock Chinese 6N1P the JSC VOSKHOD 6N1P-EB are nice upgrade and affordable. https://www.thetubestore.com/russian-6n1p https://www.partsconnexion.com/NOS-79469.html

Many feel that most of the better dealers or manufacturers will burn in tubes, not just for sound but for characteristics of matching or failure. https://www.diyaudio.com/forums/tubes-valves/195141-burned-power-tubes.html

Current 12AX7 Tubes Comparisons

You are spot on, the manufactures of "some" amplifiers goose the bias to bring up the power stated or advertised but may not result in a pleasing sound to the customer. I also refer to the Jones table as well, good information. Personally I feel after looking up your AP-900 (if I am correct) that you may benefit more with changing the 4 x 6N1 and 2 x 12AX7 if you already haven't. NOS are great and even current GL 12AX7 would really help in the holographic imaging of the amp as the GL 12AX7 excel in that department with many pieces I put them in over the last 5 years. http://www.tedweber.com/webervst/tubes1/calcbias.htm

The bias setting is generally determined by the designer / builder and listed in the owners manual of the amplifier in question. "Generally" tubes biased hot equates to stronger overall output, more bottom end but at the expensive of clean headroom and early breakup. Biasing cold the amp can become thin sounding, anemic with bass sounding a little weak but with cleaner headroom with later breakup. I like to find a place in the middle that my ears enjoy and as a rule I never go above the recommended high bias setting without first talking to the engineer of the product or at least an engineer from the company of said amp. Interesting Info On Vacuum Tube Bias