Which tubes? My amp can except El34, 6L6, KT88, an

Agree with Creeper on the 6L6s. He knows his tubes.

The 6L6 often gets over looked, because the EL34 & KT-88
get more press for their classic tube sound.

The 6L6 has better balance and a much cleaner more controled midbass, which will blend well with the solid state bass amps in your V5s.

If you amps can run them, KT-90s are also worth a listen.

Creeper and Kana, I have no problem with what you say about the sound of the 6L6, but you need to know how the powered woofers work in the Vandy 5's. The woofer amps take a speaker level signal from the main amp. They are designed this way to blend and have the same nature as the main amp. If you put in a tube that is "not the best in the low end", the low end will not be the best. I just find 6550's and EL 34's to be more linear top to bottom than the other two, and 6550's have the best bass weight and slam of the bunch. I admit that I may not be not a "classic" tube sound guy as I have been trying to rid my system of some of what I feel are limitations of the "classic" tube sound while keeping what tubes do best in my mind.

Rec's system seems very nice! I would like to hear that combo myself.I love the look of that amp too! Rec, did you have the speakers low end adjusted with that amp when they were set up?
The 5's have room compensation bass EQ built in and may be able to make up for some bass colorations of different tubes for those of you that are not as up on the 5.

Ras10, much more important than which tube you choose( as they all are good in their own way) is what you use for a X-over for the 5. Do you have the expensive model 5 x-overs? If you don't and are using the fixed value X-2's it won't matter how many different tubes you try or how much you spend on Cryo treated NOS tubes. All your signal goes through that X-over and will make or break the final result. Did you just get the amps and the speakers? Did the dealer already set up the bass EQ for you?

Maxgain, that's very interesting about how the Vandy's amps get their signal. Perhaps the 6L6 wouldn't be the best in this situation. They are cheap to experiment with though. I found the Golden Dragon KT88 to have as much bottom end as a Sovtek 6550. The Sovtek seemed a little compressed. But the Svetlana 6550 is great. Very linear. Better slam factor than the KT88.

Kana's suggestion of the KT90 is a good one too, if you can run them. Make sure you get the type 3, matched and tested. They have some quality/reliability issues, but the ones I got from Upscale Audio were very nice. They took a long, long time to burn in and settle down, perhaps 300 hours or so. But in the end, they offered a solid state like low end, and great linearity. In a Sonic Frontiers SFS-40, they outperformed a pair of bridged Adcom GFA-555's in the low end!

Creeper, the Svetlana 6550c is what I use in my amp.It was voiced with those tubes though so I leave well enough alone. I hear that in the right amp the Electro Harmonix 6550 is very good too. But it has to be the right amp! A friend tried them and a first it was great, as they burned in though the sound got real thin and nasty over the course of a few weeks. He has an ARC VT60. He asked ARC about it and they told him that they had the same results with the Electro's in the VT100. Seems to be a lot of variation in different brands, let alone different types of tubes. Makes a recomendation for someone else pretty complicated.

Maxgain, I have the Vandys low end set a 1 with the V12i. This maybe more of a room issue than an amplifier issue. I also used a Rives setup cd and a Radio Shack sound pressure meter to adjust the multiple subs settings. I like the EL34 tubes and retubed with NOS with excellent results. Good luck