Suggestions for an amp

I assume this setup is also a home theater rig?  Your speakers demand more than a HT receiver, PERIOD.  My recommendation would be to buy an integrated amplifier with a home theater bypass so you can continue to use your receiver for surround stuff but only have the stereo integrated in the loop when listening to more critical 2-channel recordings.  You change between HT and stereo with the push of one button (yes, you heard me right -- one button).  I'd HIGHLY recommend you stick a crowbar in your wallet and buy the Hegel H160 available used here now for $1600 (retail new is $3500).  You seriously won't believe how good your Silver 8s will sound, and you can go on right ahead using your RXA830 for HT.  Don't let the potential of your excellent MA speakers largely go to waste with another AVR. 

+1 @soix.
You definitely have to get a stereo integrated amp with HT bypass, even the ones that has no HT bypass feature you can always use a stereo analog audio input on the stereo integrated amp and set the volume at 80 out of 100. 80 is usually a reference for unity gain necessary for HT bypass mode.

If you need a built-in DAC in the stereo integrated amp I would highly recommend either the Rotel RA-1592 ($2500) or the new Parasound Halo Integrated ($2500 to $3k). They both have good quality sounding DAC especially for the money.
With these stereo integrated amps, not only you get much better quality amplifier section for your main front L/R speakers but you also get much better quality stereo preamp and DAC as well. For stereo music playbacks these integrated amps will sound way better than your Yamaha receiver or any receivers period.

I forgot to mention Musical Fidelity M5si stereo integrated amp ($2k) and the M6si stereo integrated amp ($3k). I highly recommend them for your Monitor Audio Silver 8 speakers. They both have USB assycrhinious DAC inputs that you can connect from your computer or NAS, etc.
These integrateds do not have a specific HT bypass input but you can use its aux analog audio input and set the volume at 80 for unity gain. 
Unity gain is basically the same as HT bypass mode. 

The Rotel RA-1592 stereo integrated amp that I also recommended to you earlier also does not have a specific HT bypass input, but you can use the aux analog audio input and set the volume at 80 and save the setting. Rotel will let you save your setting for unity gain or HT bypass input. So every time you select this input the volume on the Rotel will be disabled and fixed at 80.
So, for surround sound movies or HT use you simply control the volume and everything from your Yamaha receiver and the analog audio signal from your Yamaha receiver's front L/R channels pre-out will be routed directly to the power amplifier section of the Rotel RA-1592 integrated amp to drive your Monitor Audio Silver 8 front speakers. 

By the way, are you only doing stereo setup or surrounds (multi-channels)? 
If you're only doing stereo setup you don't even need the Yamaha receiver. You can sell it and get one of the stereo integrated amps recommended above. 
The Hegel stereo integrated that was recommended by soix is phenomenal. 

Thanks...would a Marantz PM8005 or 8006 do the trick. I've seen several reasonably priced

No, I wouldn’t get the Marantz PM8005 or 8006. Actually, the Hegel H160 stereo integrated amp that was suggested by soix earlier is currently for sale here on Audiogon for $1600. You should definitely grab it. Highly recommended! First, I didn’t realize if the Hegel H160 has digital inputs thus has built-in DAC and it has a dedicated HT bypass input as well.
Do not hesitate to buy it.

By the way, are you only doing stereo setup or multi-channels or surround setup?