How much Amp for Paradigm Studio 100 v2's

I recently bought a pair of Studio 100s and the integrated amp I hooked them up to (my early 80s era Yamaha A1 (70/80 watts @ 8/4 ohm)) causes the upper 8.5 " woofer to distort/clip at high volume. On line reviews indicate these speakers drop below 4 ohms, one suggesting a "good 4 ohm-rated amp". The speakers sound great otherwise. Do I just need a better amp to drive them?
The simple answer is that you need a high current amp not just a high wattage amp. Some examples of amps that are stable into low impedances are Sanders, H2O, Wyed4sound etc all high current other examples are Krell, Pass, Coda,Bryston, Rowland, Musical Fidelity etc.etc
Most of the high end amps people favor on this forum would fit the bill.
I would doubt that the type of the vintage amp you are using now,-have the capacity to drive low impedance speakers to high volumes with some notable exceptions of course-like McIntosh perhaps the bigger Sansuis and the mid fi "Show Off" flagship/statement pieces.
In order to get something that will let you blast your speakers you are looking at a major expense over your current amps cost.
What is your budget?
It would be helpful if you can tell us what you have heard and what you like or don't like. It would be helpful if you can tell us what you have heard and what you like or don't like.
I assume you read JA's measurements here:

Since the speaker is quite sensitive, you must be driving them pretty hard, your room is large or both. Your current amp is rated 80 watts into 4 ohms. Doubling the power into 4 ohms will get you an additional 3dB of SPL; that may or may not be enough. You could pick up a Radio Shack analog SPL meter and measure at what SPL you're over driving your amp. That would give you an idea of how much power you need.

I'd consider an ATI AT2002 or AT3002 or a Parasound A21
I had amps from 40W/channel, 90W/channel, and 125W per channel, and all sounded okay for the Paradigm Ref 100's v2 that I own. Biggest change came with the 200W Rotel 1080 - these speakers like juice and control. Think what you will about amplifier Damping Factor, but it makes a noticable difference on smaller-woofer speakers like the Paradigms in my experience. They sound much tighter, deeper, and play subjectively louder since the woofers aren't vibrating out of control (relatively speaking of course). That being said, over time the 1080 was irritating, listening fatigue from any loud volume on all but the best recordings. Cycled through some amps and stuck with the 380W/channel Rotel 1090. WOW. Even higher quality better bass, and no fatigue whatsoever at any volume. For the first time, I don't feel like the amp is running out of gas or "pushing it" when the volume is turned up very high. Effortless sound and energy to the Reference 100's. Long story short, the more current and control you give these speakers, the better they will respond.
I would consider the Parasound 2200 mk 2 as well. good sounding amp, which has tons of current for driving lower impedance speakers.