I’m sure you will enjoy the amps Glen, I believe you could use the Sansui with no issues except you will need to short pins 1 & 3 per the Atma manual (see below)
"If you use the RCA input connector, make sure a shorting jumper is installed between pins 1 & 3 on the XLR connector else a buzz may result"
The most important tubes for the sound are the driver tubes the 6SN7’s, I know you are not buying stock but the stock tubes that comes with the Atmas out of the box usually chinese Shuguang Brown Base 6SN7s are very decent, that said you could improve with NOS tubes or even some Chinese Boutique tubes, if you need more on the subject I can provide more details and I’m sure others will do as well.The power tubes "sonically" won’t provide much, not many options either, the Russian 6AS7G Svetlana’s 6H13C are very very stable, sound is magnificent and to me these are the tubes to go on this amps as far as power tubes is concerned. The NOS RCA’s 6AS7G could provide a little more power at the expense of reliability and headaches, and money too. I went that route and turned back, my MA-1’s do fine with the power offered by the Russian power tube the way Ralph designed it. If you need more details I will be happy to provide such but my advise if your speakers do fine with the Russian tubes don’t change them, I experience one of the RCA tubes heavy arcing, smoke came out of the amp (or tube) and it is very common with these tubes, IMO reliability is an issue. DO NOT USE 6AS7GA on that amp, the tube IS NOT COMPATIBLE, stay away from GE’s 6AS7G, you will run into problems.Let us know what tubes comes with the amp and I’m sure Ralph or someone else or myself will be able to help.Maybe I missed it but your speakers are sensitivity? and nominal impedance?
"If you use the RCA input connector, make sure a shorting jumper is installed between pins 1 & 3 on the XLR connector else a buzz may result"
The most important tubes for the sound are the driver tubes the 6SN7’s, I know you are not buying stock but the stock tubes that comes with the Atmas out of the box usually chinese Shuguang Brown Base 6SN7s are very decent, that said you could improve with NOS tubes or even some Chinese Boutique tubes, if you need more on the subject I can provide more details and I’m sure others will do as well.The power tubes "sonically" won’t provide much, not many options either, the Russian 6AS7G Svetlana’s 6H13C are very very stable, sound is magnificent and to me these are the tubes to go on this amps as far as power tubes is concerned. The NOS RCA’s 6AS7G could provide a little more power at the expense of reliability and headaches, and money too. I went that route and turned back, my MA-1’s do fine with the power offered by the Russian power tube the way Ralph designed it. If you need more details I will be happy to provide such but my advise if your speakers do fine with the Russian tubes don’t change them, I experience one of the RCA tubes heavy arcing, smoke came out of the amp (or tube) and it is very common with these tubes, IMO reliability is an issue. DO NOT USE 6AS7GA on that amp, the tube IS NOT COMPATIBLE, stay away from GE’s 6AS7G, you will run into problems.Let us know what tubes comes with the amp and I’m sure Ralph or someone else or myself will be able to help.Maybe I missed it but your speakers are sensitivity? and nominal impedance?