Not sure what "taking out the low bass" implies, unless you mean using an external crossover where you can filter out the low bass. I know some people use external crossovers w/ magnepans, and I think it's a mistake : particularly worse the electronic kind that have A/D & D/As in them : i.e. they take the analog signal from the preamp, turn it to digital, process it, then convert it back to analog. UGH. In general if you can avoid introducing more things in the signal path, whether extra crossovers or whatever, the better I think.
Personally, I use a REL T1 with my magnepan 1.7's, the predecessor to the T-9, mainly for home theater, though some times for rock etc where I want a bit more bottom end. The nice thing about REL's is the amp level connection so that the sub "sees" the same signal as the main L/R channels. I.e. one positive wire to each L/R is connected at the speaker binding posts, and one negative to one of those two (only need one ground). The other end has a speakon connector to the REL. At the REL end you set the crossover and volume level. This is great because it allows, as mentioned before, the sub to get the same signal as the main L/R, but also allows you to connect the main L/R DIRECT to the amp without some external crossover in the middle. It's true that you won't this way be able to filter out the lowest frequencies from the magnepans, but honestly most magnepans, including my 1.7's, don't go down super deep anyway.
This is why I and many others would recommend a REL for magnepans. If another manufacturer did the same, I'd also recommend them.
Owning both an older T1, and a newer T-5 for another system, I'd say the T-5 is faster because it's a totally sealed sub with no port or passive radiator (the T1 uses a 10 inch down-firing 10 + a 10 passive radiator). The T-5 also has a smaller driver (8"). With all that said, the T1 works pretty well w/ my Magenpan 1.7s - it certainly has plenty of bass to fill my 15 x 25 foot room. So I suspect the T-9 would also work well.
If you're room is the same size or smaller than mine, I'd say the T2 / T-7 would work just as well : maybe better. The only difference is the passive radiator is 8" vs 10". I personally think the smaller passive radiator might be better / faster. I heard a T-7 w/ Manepan 1.7's and it was a good combo in a smaller room.
Ideally I'd like a 10" SEALED sub w/ good power for my maggie 1.7 for music + HT. But a good powerful sealed large driver sub is usually quite an expensive proposition.
The main difference between the older "T" series and the newer "Serie T" seem to be improved cosmetics : i.e. beautiful glossy piano like finish to the enclosures. Not that the earlier T series wasn't attractive, for a subwoofer. Otherwise though I don't think there is any difference to the actual drivers / amp / crossover etc between the older T series or newer "Serie T".
SO : if you want to save a lot of money, get a T1 vs a T-9. Same drivers, same configuration, same amps, just a different enclosure w/ different footers. VANNs forever had a cherry T1 new for $500 (vs $1200 that a T-9 costs), and I was keeping it to myself as I was thinking of getting another to have dual subs. But sadly I don't see it available anymore on their website. As of just a week or so they did, so maybe they finally sold it, or delisted it. Might be worth calling & finding out. I did see a used one listed on Audiogon (now expired) for an asking price of $550. So you should be able to get one somewhere for $500 vs $1200 new of the T-9. Music Direct occasionally has demo REL subs - though I don't recall every seeing a T-9 for sale. I did see a T-7, but I think thats gone.
In summary : I recommend REL for magnepans, but in the entry level suggest either a used T1 / T2, or a demo T-7.
A personal usage note on my RELs : if you use the spikes, make sure they are all well planted on the floor, otherwise you will get a rattle on the really heavy bass for any that are not firmly planted. On the newer T-5, it will dance around somewhat on my hardwood floors with big booms. Spikes were not enclosed / offered. Maybe some blue tack would help......
