Hi i have platinum audio bookshelf monitors that do not sound right...

What don’t you like with your current setup?   How large is your room?  What do you listen to?  How loud? 

They might also need work on their crossover. I only say that because they're getting a little old now, and it's hard to imagine that a 7100 isn't enough to drive those speakers. 

The room is rather small, (14' X 12') 12 foot ceilings, listen to all types of music (not tooo much rap please), at moderate levels. I do however have to turn the volume up over 3/4 to get a punch !!!

Having to turn it 3/4 of the way is not an issue, it just means there is not as much gain than some other combos (your amp has adjustable gain).  Are the power guard lights on the amplifier coming on, which would signify clipping?   That amp should have enough power to cause the woofers in those speakers to bottom.   

If I were looking at an upgrade, I would be looking at the preamp, but from what you are saying, there is no issue, and no reason to upgrade unless you want to.  

I read JA’s review of the Solo’s for Stereophile. Those speakers are rated at 84db @ 6 ohms with a 5 ohm floor. The Cary SET amp JA tested was struggling to drive the Solo’s, and his conclusion was they "need a lot of amplifier watts to come alive". Your McIntosh amp is outputting approximately 125 watts @ 6 ohms with a damping factor around 150. Those are modest specs, and suggest your amp is on the low side power-wise.

Mcreyn is right, according to the amp’s Owner’s manual, your amp has adjustable gain. So if the gain switch is set to low, it’s worth experimenting with a higher setting. That said, I had a similar problem when I was driving my old Marten Coltrane Alto’s (87db @6 ohms) with a Classe Cap-2100 integrated amp. The Classe was outputting around 150 watts @ 6 ohms, but struggled to drive the Alto’s which need a lot of power. In that setup I was running the Classe pre-out to my Ayon CD-5 (as linestage). Ironically I initially set the Ayon’s gain selector to ’high’ (8v) which tripped the Classe’s protection circuitry. I had to back it off to the low setting (6v) to resolve that issue. Yet even with that (still high) gain setting, the Classe struggled. It wasn’t until I upgraded to a Boulder 1060 power amp that the Alto’s came to life. For the first time I was hearing (and feeling) deep bass, and they sounded effortless.

My hunch is your McIntosh power amp is under-powered for your speakers. I can understand it if you have a sentimental attachment to your vintage McIntosh gear, so you have two options. You could sell your Monitor Audio speakers & buy some more efficient stand mounts, or you could buy a more powerful amp. I’m personally a fan of integrated amps. You can find some very good integrateds on a limited budget. Lately there has been a bit of hooplah on ’Gon about the Hegel H360 which you can pick up in good shape 2nd hand in the low $3k range - https://www.audiogon.com/listings/lis91cg7-hegel-h360-solid-state I also saw a mint/new Hegel H190 on the ’Gon asking around $2.9k. Those amps have a very high damping factor, so they would have no problem driving your speakers. They also include a dac & streamer. Hope that helps.