I've been running an Art Audio Carissa Signature for going on a couple years with the VSM-MM w/ superbam, absolutely no problems with power delivery. Plenty of slam, bass is filled out very nicely, refined mids and highs. I beg to differ, SET's can work very nicely with even the new Merlins.
Having said that, the partnering equipment is very important. Also, as you probably know, this is not an integrated amp, I can't help you there, although the Ars-Sonum is reportedly very nice on the Merlins. I suspect the EL 34's this amp uses mates well with the Merlins. I only say this because I still occasionally use a Conrad Johnson MV-55 (el 34's, about 45 wpc), and this also works beautifully with the Merlins. I have also used Cary SLM-100 monoblocks, another amp that can use EL-34's and it too was very nice.
Having said that, the partnering equipment is very important. Also, as you probably know, this is not an integrated amp, I can't help you there, although the Ars-Sonum is reportedly very nice on the Merlins. I suspect the EL 34's this amp uses mates well with the Merlins. I only say this because I still occasionally use a Conrad Johnson MV-55 (el 34's, about 45 wpc), and this also works beautifully with the Merlins. I have also used Cary SLM-100 monoblocks, another amp that can use EL-34's and it too was very nice.