Mc 240 vs. Prima Luna

Doubling up your existing amp will not gain much. You'll have the same sound and 3db more power, just not worth the trouble. Although mono-blocks are better than stereo amps, bridging a stereo amp is not the same thing as a pure mono-block amp. A Prima Luna and perhaps some tube rolling would keep you busy for a while. 

I disagree that doubling up the current tube amp won’t gain you much. I have a pair of VAC 200iQ tube amps, and running mono is a clear and significant improvement over a single amp in stereo mode. I have 96dB / 8 ohm speakers, so the increase from 100 Watts/ch to 200 doesn’t seem like it should be meaningful. But very clearly, the pair of mono amps is much better - and it’s not always just about raw power, anyways. Also heard this same effect with the same amps in my friend’s system. And 3dB is a LOT, when you’re near your preferred listening volume in a familiar system and you’re an audiophile. "3dB isn’t much" is good forum fodder for the HT guys.

With op going from 40 to 80 watts, I’d be surprised if the improvement isn’t significant. I’d stick with the McIntosh plan.

I am a PL integrated owner for almost three years. I have used tube amplification for decades. This is the best tube amp I’ve ever owned in terms of musicality and ease-of-use. What’s especially appealing is the auto bias, ability to change power tubes for your sonic preference and the amp will shut off if one of the power tubes red plates or gets funky. To me, those features eliminated a lot of the hassle of owning a tube amplification system. I also like the sound presentation which is tonally dense with great ambience and dynamics. The power tubes can change the sonic presentation from lush and warm to robust, fast and very transparent (EL 34 versus KT150) I would say the Macintosh brand has a very appealing type of case work with its blue meters and the PrimaLuna cannot match that if that is important to you.

This model of McIntosh doesn't even have the blue meters lol. And considering non-sonic attributes, the McIntosh amps will hold value a hell of a lot better than Prima Luna. They'll basically never go down. 

@russ69

"Although mono-blocks are better than stereo amps, bridging a stereo amp is not the same thing as a pure mono-block amp." 

I agree, the key point is bridged amplifiers are not the equivalent of a true  mono block pair. 

In addition as the late almarg  would politely explain,  bridged amplifiers will see 'half' of the speaker's impedance.  8 ohm becomes 4 ohm, 4 ohm load becomes effectively 2 ohms. As a result,   the bridged amplifiers are asked to drive a more difficult impedance load.  Better to obtain genuine mono block amplifiers. 

Charles