The first question I'd ask you is what cartridge are you using?

As for the 500 series;

the 562 has a 16bit ADC @ 44.1KHz
the 565 has a 16bit ADC @ 44.1KHz
the 561 has a 20bit ADC @ 44.1KHz
the 568 has a 24bit ADC @ 44.1KHz

Vinyl doesn't have a dynamic range that requires over 16bits, getting the level right (just below clipping on the ADC) is much more important.

It has been said that different recordings are at different levels, this is also true in the digital domain, hence the 518. A novel and quite elegant way of controlling the level into a ADC like the MPMAX221 would be a Meridian 101 (or 101B).

Using the 101(B) would give you an excellent phono stage and the ability to control the level into the ADC.

The 101 preamp is readily available second hand, has a nice small form factor and has a modular design so different cartridges can be accommodated.

I believe a 101 into a basic 562 would sound better than a non level controlled phono stage into the MPMAX221.

Steve.