that vs115 is fine, there are other models too, slightly older or newer, that will do well with the m-l speakers... i do think it would be wise to get an arc model that, like the vs115, runs 4 power tubes per channel... that will be in the 100 wpc range, a good step up in drive power from the small bernings (30 wpc) that you said were inadequate
other arc models to consider would be vt100 series and so on... see examples below (do your homework, i am not vouching for those particular sellers, and make sure the tubes are pretty fresh)
https://www.usaudiomart.com/details/650222704-audio-research-vs-110/
https://www.usaudiomart.com/details/650269341-audio-research-reference-110-mono-amplifiers/
https://www.usaudiomart.com/details/650202175-audio-research-vt-100-mk3-tube-amplifier/