What was your source? Your iPhone? Is your iPhone enough to drive the MS1's? If yes, it'd be nice to know how the iPhone HO matches up against the GVPT.

Thanks for the review--I've been curious about tube amps and portable tube amps especially.

@Kiteki
The source I was using was an iPod Touch G4 - but it's pretty much same out of the iPhone4 as well. The iPhone4 drives the MS1is just fine - about 65-70% volume is about as loud as I like to go. Through the iPhone4 (listening to Clapton Unplugged (Layla) - the sound is sparkly, mids are forward, and it is very pleasant. Nice bass impact (my Alessandros are vented). Bringing the Porta Tube into the chain, the whole sound suddenly gains more warmth, body and texture. The highs are still there, it's still sparkly - but it just sounds more "real". I feel as though I'm there. Bass has a touch more authority - but I may not have these volume matched (I'm doing it by ear).
I personally think both the iPod Touch G4 and iPhone4 are very good sources - but the GVPT takes this to a new level for me. I'm thinking a lot of people may not necessarily appreciate the difference - but for me, it is the signature I've been looking for over the past 12 months. It is magic - and it's why I bought it. Your own mileage may vary. I'd encourage others to try first before shelling out this sort of money though.
@metalsonata - thanks. I was always curious about tubes - and no doubt this may lead to a more permanent desktop tube amp down the track - but for now the GVPT is all I need.

Wow you bought it? I thought you were just reviewing a demo unit being sent around =)

I tried this unit myself very briefly in a store in Singapore.

Yep - was reviewing it - ended up buying it. Perfect match to the MS1i.

Ok, thx 4 review.