Graham and Shelter matching - and other arms/carts

When you get a component that truly lifts your system up and reveals what's going on everywhere else, you learn things about your system that you hadn't realized before. My new Io Sig has shown me that I probably need a better linestage (I posted about this in Amps/Preamps), and it's also taught me something about arm/cart matching.

Now that the Io is in the system, I am hearing an unhappy balance between my Graham 2.2 tonearm and Shelter 901 cartridge. There's a tubby bass resonance that sounds to me like the Shelter cantilever feeding back into the unipivot arm structure. The outriggers on the Graham are supposed to minimize this effect, but perhaps the match just simply isn't made in heaven.

Instead, my Ortofon RS-212 tonearm, matched with Ortofon SPU Classic GM cart, is sounding much more balanced, real and musical.

That leaves me with the question of what to do with my Graham and Shelter. I'd like to have a "modern" arm/cart combo to compare with the classic Ortofon setup (I currently have 3 arms mounted on my table). My third arm is an Origin Live modified RB250, which currently has a Denon 103R mounted on it (probably not the perfect matchup either). The Shelter doesn't sound fantastic in the Rega - it's better in the Graham.

I do like the Shelter sound a lot, so I could buy an arm that's a more appropriate match for it, a Moerch perhaps. But I'd have to sell the Graham to afford that, and I kind of want to keep a unipivot.

Any recommendations for exchanging the Shelter and Denon for carts more appropriate for the Rega and Graham, or vice-versa?
The Io Sig is a great piece and it has to be frustrating to have added such and then experienced "less". Your comments regrading the Graham/Shelter are surprising. I have heard the 901 and the 501 on a 2.2 and certainly didn't hear the results that you are getting. While perhaps not the ultimate match with the Graham, they sounded great. In fact, it is my understanding that one of the guys at Musical Surroundings enjoyed the 901 in his Graham to the extent that they considered (or are considering) pursuing the brand in their line.
Try a ZYX R-100 Fuji or a R-1000 Airy. Better compliance match and superb cartridges.
Perhaps a Clearaudio virtuoso wood mkII on the unipivot? (good compliance match). . .
Dear friend: I use the Shelter with: SME IV, Micro Seiki MAX 282 and Dynavector DV 505. Great with all these tonearms.
Oh, I'd love to afford a ZYX for my 2.2 so that I could give you my impressions! :-)