I recently upgraded the factory stereo in my '02 Lexus IS300 to the new JVC XR-KW810, and thought I'd share my experiences thus far.
I didn't really want to swap out the factory stereo, as it still sounded (and looked) quite good. Unfortunately, I recently picked up the official Google car dock for my Nexus One, and really wanted to use it as a music player in the car. Since the Google dock only has Bluetooth audio output, my only options for the factory Lexus stereo were to use the headphone jack on the phone to a tape adapter or a yet-to-be-hacked-in aux input. I tried it with a tape adapter for a couple of days, and decided it was time for a Bluetooth-capable stereo. My only requirements were Bluetooth, an aux-in, double-DIN with a real volume knob (and preferably lots of other "hard" buttons), and custom color configuration (to more closely match the IS300's orange illumination). This led me to the JVC XR-KW610 and it's bigger brother, the XR-KW810. The 610 was okay, but the segmented display looked kinda hokey and it didn't come with the Bluetooth adapter in-box. The 810 has a better looking matrix display and Bluetooth is included. Done.
Installation was very smooth (at least around the head unit itself- reusing the Lexus factory amp and speakers on a non-Lexus head requires a special part). It includes a sleeve for "roll your own" setups as well as an assortment of screwholes in the unit itself. The included Bluetooth adapter just plugs into the rear USB port (there's also one on the front), and the handsfree mic hangs off the back. The unit has a headlight switch input, which is pretty handy for dimming the illumination when the headlights are on. After putting the car all back together and booting it up, my first impressions were pretty good.
Sound quality through my factory amp was quite solid, though the default EQ settings were a little bassy on my setup (I didn't try the unit's built-in amp). This was easily rectified by tweaking the ProEQ settings, which allow for finer unit-wide EQ adjustment (as opposed to the front-panel EQ settings, which are per-input and fairly coarse). In addition to the ProEQ settings, there's a decent array of loudness, LPF, HPF, amp and sub gain adjustments. Also, each source's gain can be adjusted individually.
The controls are generally intuitive and pretty easy to operate without looking. There's a four-way button on the lower left of the face, three large buttons next to the volume knob, source/power and EQ buttons, and 6 preset selector buttons. The buttons are large, but have a somewhat cheap feel. The glossy finish on the unit looks nice under low light, but shows every smudge and speck of dust on a sunny day. The illumination color adjustments are extensive - buttons and display can be colored independently, and different colors can be set for day and night profiles. The display can be difficult to read in direct sunlight, though it does have a polarizing layer that helps somewhat. The real low point on the display is the low LCD update frequency, which causes horizontal text scrolling on long titles or RDS messages to be difficult to read.
On the initial install, I hadn't purchased the separate KT-HD300 HD Radio tuner yet. FM reception on the built-in tuner was quite good, but AM was a little weak compared the the factory unit. The one thing I missed from the factory head was RDS display (station ID and "now playing" info), which the built-in tuner doesn't have. However, the HD tuner adds this, so I ordered it (online, $89). The external HD tuner disables and replaces the built-in tuner by plugging into the back of the head unit. Luckily, it includes long antenna, power and data cables, because it's rather bulky (about 5x9x1 inches)- it took a bit of creativity to find a niche for it. It works as advertised, and does a seamless "upgrade" to the digital signal once it's locked in on the analog. Direct tuning to an digital-only station (ie, via a preset) can take a couple of seconds- the display flashes "Linking" while this is occurring. My only other beef with the HD tuner is a pretty minor one: it disables the "up/down" controls for scanning through presets that are available with the stock tuner (with the HD tuner, up/down is used to switch between HD channels on the same station). The unit supports 18 presets on the FM band, but only 6 are accessible by hard button. Without the up/down access, presets are selected by tapping the menu button, turning the knob to select, and tapping the knob. It works, but nowhere near as conveniently as with the built-in tuner.
The Bluetooth support is fairly advanced compared to other units in the same price range- it supports A2DP, AVRCP 1.3, HSP/HFP and PBAP. In English, this means you can use it to listen to high-quality audio from your music player, remotely control it, get the "now playing" info, navigate playlists, voice dial your cell-phone and answer calls, and copy or navigate the phonebook from the unit. I've only been able to try parts of this thus far, as the Nexus One's Bluetooth implementation doesn't yet support all this functionality. What I have tried is pretty solid- the unit can pair with two different devices, and has a dedicated call/answer button on the face. The handsfree mic volume seems a little low, so it needs to be routed pretty close to your face (maybe the visor). I use the Nexus One car dock for my handsfree calling anyway, so it's not an issue for me.
The USB support is pretty complete as well. If using a thumb drive, it has full folder navigation support and displays album/title info while playing. It also supports USB iPod control and charging, which works quite well, supporting standard functions (playlists, artist/album/song, podcasts, etc). It does disable the iPod display and control (shows a nifty "JVC"), so you have no choice but to control the music from the head unit (difficult for the backseat DJs, though they could use the included remote control in a pinch).
The CD player is pretty standard- it supports CD-TEXT, so newer CDs or burned ones will display title and track info. Not much else to say here.
Thus far, I'm very pleased with the JVC XR-KW810 head unit and KT-HD300 HD tuner. Now if Google would get around to updating the Bluetooth stack to support AVRCP 1.3, I could use all the goodies over Bluetooth.