Hi Herb,

Here are a couple of my thoughts. I have a pair of UFO25s configured as balanced monos and they are absolutely positively amazing. So, on the one hand I want to give you an unqualified, unhesitating recommendation to go for it. And if the only difference between your two UFOs is the stepped attenuator vs. standard volume pot I don't necessarily think that is a problem. But more on that below.

But, your situation raises some questions for me, starting with why do you want two? If you want to run them balanced then I totally understand, and see above for unqualified, unhesitating recommendation. But I'm guessing if that were your plan you would have mentioned it. Do you just want a couple more watts? Klipsch isn't my thing but I'm pretty sure the La Scalas are crazy sensitive, yes? So sensitive that a single UFO25 ought to be plenty of watts to give you all the sound you want. And if they don't, another UFO25 (or swapping the '25 for Sarah) is only going to get you 3 dB. Is that really the difference you're looking for?

And the other question is do you know that the volume pot is the only difference between the two amps? i.e. do they have the same caps and resistors? Also, while the sonic difference between the stepped attenuator and pot is probably pretty small, the issue would be if you use volume control on the amp for your main volume control. I think the steps on the stepped attenuator are probably too big to be useful for you main system volume control. I have stepped attenuators on mine, but use my preamp for volume control. You can always send one or both back to Decware and get them matched (and the warranty transferred) but that is another layer of cost and complexity to consider. And of course 2 amps means you'll need twice as many tubes going forward as well.

Hope this helps.

Hey HERBERT….I’m going to throw my hat into the ring for running a pair of mono blocks.  I have a pair of SE84C+ Monoblocks that were upgraded with with 25th anniversary modifications and the UFO transformers.  I did have mine matched to have the same internals.  I do love them for having the ability to independently control the volume on the left and right speakers for channel balancing in my room which is not treated.  The amps kick ass, and have plenty of power to run my ERR speakers with some headroom in reserve.  

Depending on how loud you like to listen to music… Adding a second amp to your system may allow you to lower the volume on each amp which would not push the tubes as hard and let them last longer in theory.  While you would have to commit to buying twice the amount tubes as opposed to running a single amp… I don’t know how the law of diminishing returns would be by comparison in terms of cost for running a pair vs a single amp.  

I’ve never heard the Rachel, but if it’s just wanting more power, then maybe the Rachel is a viable option since you are getting 6 watts with a Rachel as opposed to 2.3 watts with the UFO25.  I have heard the UFO25 at Decfest, so if it was me…I would say that if cost wasn’t an issue…buy a second UFO25.  With those Klipsch speakers and a pair of monoblocks would really rock the house being super efficient.

Good luck and keep us posted on which way you go.

Dom